Biologic replacement for fibrin clot

ABSTRACT

The invention provides composition and methods for repairing a ruptured anterior cruciate ligament.

CLAIM OF PRIORITY

This application is a continuation application which claims benefitunder 35 U.S.C §120 of U.S. application Ser. No. 14/157,854 filed onJan. 17, 2014, entitled “BIOLOGIC REPLACEMENT FOR FIBRIN CLOT,” nowabandoned which is a continuation of U.S. application Ser. No.13/449,449 filed on Apr. 18, 2012, entitled “BIOLOGIC REPLACEMENT FORFIBRIN CLOT,” now U.S. Pat. No. 8,642,735, which is a continuation ofU.S. application Ser. No. 13/215,369 filed on Aug. 23, 2011, nowabandoned, which is a continuation application which claims benefitunder 35 U.S.C §120 of U.S. application Ser. No. 12/900,216 filed onOct. 7, 2010, now abandoned, which is a divisional application whichclaims benefit under 35 U.S.C. §121 of U.S. application Ser. No.11/092,992 filed on Mar. 29, 2005, now U.S. Pat. No. 7,838,630, which isa continuation application which claims benefit under 35 U.S.C §120 ofU.S. application Ser. No. 09/917,058 filed on Jul. 27, 2001, now U.S.Pat. No. 6,964,685, which is a continuation-in-part application whichclaims benefit under 35 U.S.C §120 of U.S. application Ser. No.09/594,295 filed Jun. 15, 2000, now abandoned, which claims benefitunder 35 U.S.C §119(e) of U.S. Provisional Application Ser. No.60/182,972, filed Feb. 16, 2000, and 60/140,197, filed Jun. 22, 1999,the contents of each of which are herein incorporated by reference intheir entireties.

GOVERNMENT SUPPORT

This invention was made with government support under Grant No.: R03AR46356 awarded by the National Institutes of Health (NIH). Thegovernment has certain rights in the invention.

FIELD OF THE INVENTION

This invention relates generally to compositions and methods forrepairing injured intra and extra-articular tissue.

BACKGROUND INFORMATION

Intra-articular tissues, such as the anterior cruciate ligament (ACL),do not heal after rupture. In addition, the meniscus and the articularcartilage in human joints also often fail to heal after an injury.Tissues found outside of joints heal by forming a fibrin clot, whichconnects the ruptured tissue ends and is subsequently remodeled to formscar, which heals the tissue. Inside a synovial joint, a fibrin cloteither fails to form or is quickly lysed after injury to the knee, thuspreventing joint arthrosis and stiffness after minor injury. Jointscontain synovial fluid which, as part of normal joint activity,naturally prevent clot formation in joints. This fibrinolytic processresults in premature degradation of the fibrin clot scaffold anddisruption of the healing process for tissues within the joint or withinintra-articular tissues.

The current treatment method for human anterior cruciate ligament repairafter rupture involves removing the ruptured fan-shaped ligament andreplacing it with a point-to-point tendon graft. While this procedurecan initially restore gross stability in most patients, longer follow-updemonstrates many post-operative patients have abnormal structurallaxity, suggesting the reconstruction may not withstand the physiologicforces applied over time (Dye, 325 Clin. Orthop. 130-139 (1996)). Theloss of anterior cruciate ligament function has been found to result inearly and progressive radiographic changes consistent with jointdeterioration (Hefti et al., 73A(3) J. Bone Joint Surg. 373-383 (1991)).As anterior cruciate ligament rupture is most commonly an injury of ayoung athletes, early osteoarthritis in this group has difficultconsequences.

Thus, there is a need in the orthopedic art for a device that reproducesthe function of the fibrin clot to re-connect extra-articular tissues inthe early phase of healing. A therapeutic intervention that wouldfacilitate anterior cruciate ligament regeneration or healing couldoffer several advantages over anterior cruciate ligament reconstruction.With anterior cruciate ligament regeneration or healing, the fan-shapedmultiple fascicle structure could be preserved, the complex bonyinsertion sites could remain intact, and the proprioceptive function ofthe ligament could be retained.

SUMMARY OF INVENTION

The invention provides a composition of collagen, an extracellularmatrix protein, and a platelet. The invention further provides acomposition of collagen, a platelet and a neutralizing agent, e.g.sodium hydroxide or hydrochloric acid.

Further provided by the invention is a tissue adhesive composition ofcollagen, an extracellular matrix protein, and a platelet formulated forthe administration to a patient. Additionally, the invention provides acomposition of collagen, a platelet and a neutralizing agent, e.g.sodium hydroxide or hydrochloric acid formulated for the administrationto a patient. The patient is preferably a mammal. The mammal can be,e.g., a human, non-human primate, mouse, rat, dog, cat, horse, or cow.In various aspects the platelet is derived from the patient. In otheraspects the platelet is derived from a donor that is allogeneic to thepatient.

The collagen can be of the soluble or the insoluble type. Preferably,the collagen is soluble, e.g., acidic or basic. For example the collagencan be type I, II, III, IV, V, IX or X. Preferably the collagen issoluble. More preferably the collagen is soluble type I collagen. Anextracellular matrix protein includes for example elastin, laminin,fibronectin and entectin.

The compositions of the invention can additionally include plasma. Insome aspects, the plasma is derived from the patient. In other aspectsthe plasma is derived from a donor that is allogeneic to the patient.

Alternatively, the composition includes one or more additives, such asinsoluble collagen, a growth factor, a cross-linking agent, a stem cell,a genetically altered fibroblast and a cell media supplement. Growthfactor includes for example, platelet derived growth factor-AA(PDGP-AA), platelet derived growth factor-BB (PDGF-BB), platelet derivedgrowth factor-AB (PDGF-AB), transforming growth factor beta (TGF-β),epidermal growth factor (EGF), acidic fibroblast growth factor (aFGF),basic fibroblast growth factor (bFGF), insulin-like growth factor-1(IGF-1), interleukin-1-alpha (IL-1α), and insulin.

By cross-linking agent is meant that the agent is capable of formingchemical bonds between the constituents of the composition. Thecross-linking agent can be for example, a protein or a small molecule,e.g., glutaraldehyde or alcohol.

Cell media supplement is meant to include for example glucose, ascorbicacid, antibiotics, or glutamine.

The invention provided methods of treating an intra-articular injury ina subject, by contacting the ends of a ruptured tissue from the subjectwith a composition of the invention. Intra-articular injuries includefor example a meniscal tear, ligament tear or a cartilage lesion.

The invention further provides a method of treating an extra-articularinjury in a subject, by contacting the ends of a ruptured tissue fromthe subject with a composition of the invention. Extra-articularinjuries include for example, injuries of the is ligament, tendon, boneor muscle.

In some aspects the methods further include mechanically joining theends of the ruptured tissue, e.g., suturing.

The invention provides devices (e.g., tissue-adhesive composition) andmethods for promoting a connection between the ruptured ends of thetissue and fibers after injury, by encouraging the migration ofappropriate healing cells to form scar and new tissue in the device. Thedevice is a bioengineered substitute for the fibrin clot and isimplanted between the ruptured ends of the ligament fascicles. Thissubstitute scaffold is designed to stimulate cell proliferation andextracellular matrix production in the gap between the ruptured ends ofthe anterior cruciate ligament, thus facilitating healing andregeneration. The device resists premature degradation of thereplacement clot by the intra-synovial environment.

In one embodiment, the invention provides a three-dimensional (3-D)scaffold composition for repairing a ruptured anterior cruciate ligament(ACL) and a method for attaching the composition to the rupturedanterior cruciate ligament. The scaffold composition includes aninductive core, made of collagen or other material, and is surrounded bya layer critical to the attachment of the core to the surroundingtissue, called the adhesive zone. After the scaffold composition isinserted into the region between the torn ends of the anterior cruciateligament and adhesively attached to the ends of the ligament, theadhesive zone provides a microenvironment for inducing fibroblast cellsfrom the anterior cruciate ligament to migrate into the scaffold. Aftermigrating into the inductive core of the scaffold, the fibroblast cellsconform to the collagen structure between the ligament and heal the gapbetween the ruptured ends.

The invention also includes the use of a collagen-based glue as anadhesive to maintain contact between the torn edges of the meniscus. Thetorn edges of the meniscus are pretreated to expose selectedextracellular matrix components in the meniscus. Then, the glue isintroduced into the tear. Bonds are formed between the extracellularmatrix in the meniscal tissue and the material of the glue. The bondsform a bridge across the gap in the meniscus. This adhesive zone bridgecan then induce the migration of cells to the bridge, which is thenremodeled by the meniscal cells, thus healing the tear.

This invention further includes the use of a collagen-based scaffold asan adhesive, e.g. tissue-adhesive composition (as well as a cellmigration inducer) to maintain and restore contact between the torncartilage and the surrounding cartilage and bone. The torn edges arepretreated to expose the extracellular matrix components in thecartilage. A collagen scaffold (e.g. tissue-adhesive composition) isthen introduced into the tear. Bonds are formed between theextracellular matrix of the torn tissue and the material of the glue.The bonds form a bridge across the gap in the articular cartilage. Thisadhesive zone bridge can then induce the migration of cells to thebridge, which is remodeled by the cartilage cells, thus healing theinjured area.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although methods and materialssimilar or equivalent to those described herein can be used in thepractice or testing of the present invention, suitable methods andmaterials are described below. All publications, patent applications,patents, and other references mentioned herein are incorporated byreference in their entirety. In case of conflict, the presentspecification, including definitions, will control. In addition, thematerials, methods, and examples are illustrative only and not intendedto be limiting.

Other features and advantages of the invention will be apparent from thefollowing detailed description, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a replacement clot with an inductivecore and an adhesive zone.

FIG. 2 is a schematic drawing of the bonding between fibers as anattachment mechanism.

FIG. 3 is a schematic drawing of bonding between the inductive core andthe tissue by maintaining mechanical contact.

FIG. 4 is a schematic of tissue allocation for explants for2-dimensional (2-D) and 3-dimensional (3-D) migration constructs.

FIG. 5 is a schematic of test and control 3-dimensional (3-D) constructsviewed from the top.

FIG. 6 is a graph depicting the effective radius of outgrowth as afunction of time from initial observed outgrowth for human anteriorcruciate ligament (ACL) explants (n=24, values are mean±SEM).

FIG. 7 is a histogram demonstrating the changes in cell density in thefascicle-collagen-glycosaminoglycan (CG) scaffold construct as afunction of time in culture (values are the mean±SEM).

FIG. 8 is a histogram of the maximum cell number density in thecollagen-glycosaminoglycan scaffold as a function of weeks in culture(values are mean±SEM).

FIG. 9 is a histogram showing the cell densities incollagen-glycosaminoglycan (CG) matrices into which cells from explantsfrom femoral, middle, and tibial zones of ruptured anterior cruciateligaments migrated and proliferated after 1, 2, 3, and 4 weeks inculture. (Values are the mean±SEM).

FIG. 10 is a histogram showing migration into acollagen-glycosaminoglycan (CG) scaffold from explants of intact andruptured human anterior cruciate ligaments.

FIG. 11 is a histogram showing the cell number density near the site ofrupture in the human anterior cruciate ligament as a function of timeafter injury.

FIG. 12 is a schematic of tissue allocation for explants for2-dimensional (2-D) and 3-dimensional (3-D) migration constructs.

FIG. 13 is a histogram demonstrating changes in cell number density nearthe site of injury as a function of time after complete anteriorcruciate ligament rupture and comparison with the cell number density inthe proximal unruptured anterior cruciate ligament. Error bars representthe standard error of the mean (SEM).

FIG. 14 is a histogram demonstrating the changes in blood vessel densitynear the site of injury as a function of time after complete anteriorcruciate ligament rupture and comparison with the blood vessel densityin the proximal unruptured anterior cruciate ligament. Error barsrepresent the standard error of the mean (SEM).

FIGS. 15A-15D are schematics of the gross and histologic appearance ofthe four phases of the healing response in the human anterior cruciateligament. FIG. 15A shows the inflammatory phase showing mop-ends of theremnants (a), disruption of the epiligament and synovial covering of theligament (b), intimal hyperplasia of the vessels (c) and loss of theregular crimp structure near the site of injury (d). FIG. 15B shows theepiligamentous regeneration phase involving a gradual recovering of theligament remnant by vascularized, epiligamentous tissue and synovium(e). FIG. 15C shows the proliferative phase with a revascularization ofthe remnant with groups of capillaries (f). FIG. 15D shows theremodeling and maturation stage characterized by a decrease in cellnumber density and blood vessel density (g), and retraction of theligament remnant (h).

FIG. 16 is a histogram of the maximum cell number density in thecollagen-glycosaminoglycan template as a function of explant harvestlocation (values are mean+SEM).

FIG. 17 is a histogram of the effect of location on outgrowth rate forhigh and low serum concentration.

FIG. 18 is a histogram for outgrowth rates from human anterior cruciateligament explants as a function of location and TGF-β concentration.

FIG. 19 is a histogram showing maximum cell number density in thecollagen-glycosaminoglycan scaffold as a function of time in culture.

FIGS. 20A and 20B are drawings illustrating preparation of the molds.

FIGS. 21A-21D are photomicrographs of the collagen gel with human ACLcells demonstrating increasing cell number density and increasingcellular alignment with time in culture. All micrographs are at 200×.

FIG. 22 is a drawing illustrating the position of the explanted ACLtissue in the mold.

FIG. 23 is a graph illustrating gel contraction with time in the gelwith cells and the gel without cells.

FIG. 24 is a photomicrograph of the interface between the ACL tissue(explant) and the gel in both the cell-gel and the cell-free gel after21 days in culture.

FIG. 25 is a photograph of a mold with mesh at one end and a needle tosecure tissue at the other end.

FIG. 26 is a graph illustrating minimum gel widths for the four groupsduring the four weeks of culture.

FIG. 27 is a photomicrograph of the PRP gel at 1 mm from the explantedACL tissue.

FIG. 28 is a histogram demonstrating cell proliferation in a collagenscaffold with the addition of selected growth factors.

FIG. 29 is a histogram demonstrating the effect of “growth factorcocktail” (GFC) concentration on retention of DNA in the ACL seeded gelsafter three weeks in culture.

DETAILED DESCRIPTION

The invention provides compositions, e.g. a tissue-adhesive compositionthat are useful for repairing injured intra and extra-articular tissue.For example the compositions can be used in the repair of many tissueswithin articular joints, including the anterior cruciate ligament, kneemeniscus, glenoid labrum, and acetabular labrum. Additionally, thecompositions can be used to repair bone fractures, especially where thebone fractures are located in an intra-articular environment.

The compositions of the invention, can be incorporated intopharmaceutical compositions and administered to a subject.

The invention also provides methods of treating intra and extraarticular injuries in a subject, e.g., mammal by contacting the ends ofa ruptured tissue from the subject with the compositions of theinvention. Intra-articular injuries include for example, meniscal tears,ligament tears and cartilage lesion. Extra-articular injuries includefor example injuries to the ligament, tendon or muscle.

The device and compositions of the invention promotes regeneration ofthe human anterior cruciate ligament. Regeneration offers severaladvantages over reconstruction, including maintenance of the complexinsertion sites and fan-shape of the ligament, and preservation ofremaining proprioceptive fibers within the ligament substance. Theinvention provides a scaffold (e.g., tissue adhesive compositions) whichthe patient's body can develop a network of capillaries, arteries, andveins. Well-vascularized connective tissues heal as a result ofmigration of fibroblasts into the scaffold. Wound closure issubsequently facilitated by a contractile cell. The invention alsopermits the re-enervation of the damaged area by providing a cellularsubstrate for regenerating neurons.

The advantages of the invention also include (1) a less invasivetreatment as compared with the current techniques, which involvedrilling into the bone; (2) faster surgery (as opposed to currentmeniscal repair techniques); (3) no donor site morbidity (as is seenwith harvesting tendon grafts); (4) a quicker healing time; (5) agreater likelihood of the restoration of the normal function of theligament (because the collagen scaffold is repopulated by the patient'sown ligament cells); and (6) restoration of the meniscal structure (ascontrasted with meniscectomy) or the articular cartilage structure (ascontrasted with total joint arthroplasty). Implanting a device thatfacilitates the migration of the patient's own cells to the injured area(1) eliminates the waiting time for ex vivo cell culture; (2) takesadvantage of local nutritional sources and blood supply; (3) avoids theneed for a second procedure; and (4) avoids the sudden change innutritional environment seen by cells transferred from laboratoryculture into a patient (see, Ferber, 284(5413) Science 422-425 (1999);Ferber, 284(5413) Science 423 (1999)).

Inductive Core.

Referring to the drawings, a biological replacement fibrin clot of theinvention is shown in FIG. 1. The replacement fibrin clot includes acentral inductive core surrounded by an adhesive zone.

The inductive core is preferably made of a compressible, resilientmaterial which has some resistance to degradation by synovial fluid. Theinductive core member may be made of either permanent or biodegradablematerials.

Scaffolds that make up the inductive core may function either asinsoluble regulators of cell function or simply as delivery vehicles ofa supporting structure for cell migration or synthesis. Numerousmatrices made of either natural or synthetic components have beeninvestigated for use in ligament repair and reconstruction. Naturalmatrices are made from processed or reconstituted tissue components(such as collagens and GAGs). Because natural matrices mimic thestructures ordinarily responsible for the reciprocal interaction betweencells and their environment, they act as cell regulators with minimalmodification, giving the cells the ability to remodel an implantedmaterial, which is a prerequisite for regeneration.

Many biological materials are available for making the inductive core,including collagen compositions (either collagen fiber or collagen gel),compositions containing glycosaminoglycan (GAG), hyaluran compositions,and various synthetic compositions. Collagen-glycosaminoglycan (CG)copolymers have been used successfully in the regeneration of dermis andperipheral nerve. Porous natural polymers, fabricated as sponge-like andfibrous scaffolds, have been investigated as implants to facilitateregeneration of selected musculoskeletal tissues including ligaments.Preferably the inductive core is soluble type I collagen, anextracellular matrix protein and a platelet.

An important subset of natural matrices are those made predominantlyfrom collagen, the main structural component in ligament. Type Icollagen is the predominant component of the extracellular matrix forthe human anterior cruciate ligament. As such, it is a logical choicefor the basis of a bioengineered scaffold for the inductive core.Collagen occurs predominantly in a fibrous form, allowing design ofmaterials with very different mechanical properties by altering thevolume fraction, fiber orientation, and degree of cross-linking of thecollagen. The biologic properties of cell infiltration rate and scaffolddegradation may also be altered by varying the pore size, degree ofcross-linking, and the use of additional proteins, such asglycosaminoglycans, growth factors, and cytokines. In addition,collagen-based biomaterials can be manufactured from a patient's ownskin, thus minimizing the antigenicity of the implant (Ford et al., 105Laryngoscope 944-948 (1995)).

Porous collagen scaffolds of varying composition and architecture havebeen researched as templates for regeneration of a variety of tissuesincluding bone, skin and muscle. A porous collagen-glycosaminoglycan(CG) scaffold has been used successfully in regeneration of dermis(Yannas et al., 86 Proc. Natl. Acad. Sci. USA 933-937 (1989)) andperipheral nerve (Chamberlain, Long Term Functional And MorphologicalEvaluation Of Peripheral Nerves Regenerated Through Degradable CollagenImplants (M.S. Thesis Massachusetts Institute of Technology, 1998)(onfile with the MIT Library)).

Recent work has focused on the use of collagen fibers, to serve asscaffolds for the regeneration of the anterior cruciate ligament. Thecurrent design of these prostheses is as a substitute for the entireanterior cruciate ligament, that is the ruptured anterior cruciateligament is removed from the knee and replaced by a point-to-pointcollagen graft (Jackson, 24 Am. J. Sports Med. 405-414 (1996)). Unlikethe devices of the invention, these methods do not allow for thepreservation of the complex geometry and insertion sites of the anteriorcruciate ligament. These devices also require removal of theproprioceptive innervation of the anterior cruciate ligament. Thedevices of the invention, which facilitate the regeneration of defectcaused by rupture while retaining the remainder of the rupturedligament, would thus have potential advantages over the previousdevices. Moreover, no studies to date have specifically investigated theuse of any of these materials to serve as a provisional scaffold afterprimary repair of the anterior cruciate ligament, as provided by thisinvention.

Synthetic matrices are made predominantly of polymeric materials.Synthetic matrices offer the advantage of a range of carefully definedchemical compositions and structural arrangements. Some syntheticmatrices are not degradable. While the non-degradable matrices may aidin repair, non-degradable matrices are not replaced by remodeling andtherefore cannot be used to fully regenerate ligament. It is alsoundesirable to leave foreign materials permanently in a joint due to theproblems associated with the generation of wear particles, thus onlydegradable materials are preferred for work in regeneration. Degradablesynthetic scaffolds can be engineered to control the rate ofdegradation.

The inductive core can be composed of foamed rubber, natural material,synthetic materials such as rubber, silicone and plastic, ground andcompacted material, perforated material, or a compressible solidmaterial. For example, the inductive core can be made of (1) aninjectable high molecular weight poly(propylene fumarate) copolymer thathardens quickly in the body (Peter et al., 10(3) J. Biomater. Sci.Polym. Ed. 363-73 (1999)); (2) a bioresorbable poly(propylenefumarate-co-ethylene glycol) copolymer (Suggs et al., 20(7) Biomaterials683-90 (1999)); (3) a branched, porous polyglycolic acid polymer coatedwith a second polylactide-coglycolide polymer (Anseth et al., 17(2)Nature Biotechnol. 156-9 (1999)); or (4) a polyglycolic acid polymer,partially hydrolyzed with sodium hydroxide to create hydrophilichydroxyl groups on the polymer that enable cells to attach (see,Niklason et al., 284 Science 489-493 (1999)). The latter material hasbeen used as a scaffold for construction of bioartificial arteries invitro.

The inductive core can be any shape that is useful for implantation intoa patient's joint, including a solid cylindrical member, cylindricalmember having hollow cavities, a tube, a flat sheet rolled into a tubeso as to define a hollow cavity, liquid, or an amorphous shape whichconforms to that of the tissue gap.

The inductive core may incorporate several different materials indifferent phases. The inductive core may be made of a gel, porous ornon-porous solid or liquid material or some combination of these. Theremay be a combination of several different materials, some of which maybe designed to release chemicals, enzymes, hormones, cytokines, orgrowth factors to enhance the inductive qualities of the inductive core.

Alternatively, the inductive core and adhesive zone can form a singlecontinuous zone, either before insertion into the intra-articular zoneor after insertion. Preferably, the inductive core and the adhesive zoneis a single zone.

The inductive core may be seeded with cells. Furthermore, the cells cangenetically altered to express growth factors or other chemicals.

Growth Factors.

The effects of several growth factors on cultures of ligament cells havebeen reported, such as platelet derived growth factor-AA (PDGP-AA),platelet derived growth factor-BB (PDGF-BB), platelet derived growthfactor-AB (PDGF-AB), transforming growth factor beta (TGF-β), epidermalgrowth factor (EGF), acidic fibroblast growth factor (aFGF), basicfibroblast growth factor (bFGF), insulin-like growth factor-1 (IGF-1),interleukin-1-alpha (IL-1α), and insulin (see, DesRosiers et al., 14 J.Orthop. Res. 200-9 (1996); Schmidt et al., 13 J. Orthop. Res. 184-90(1995); Spindler et al., 14 J. Orthop. Res. 542-6 (1996)).

Adhesive Zone.

As shown in FIG. 1, the adhesive zone maintains contact between theinductive core and the patient tissue to promote the migration of cellsfrom tissue into the inductive core.

Many of the same materials used to make the inductive core can also beused to make the adhesive zone. The adhesive zone may be made ofpermanent or biodegradable materials such as polymers and copolymers.The adhesive zone can be composed, for example, of collagen fibers,collagen gel, foamed rubber, natural material, synthetic materials suchas rubber, silicone and plastic, ground and compacted material,perforated material, or a compressible solid material.

The adhesive zone can also be any shape that is useful for implantationinto a patient's joint.

The contact between the inductive core and the surrounding tissue can beaccomplished by formation of chemical bonds between the material of thecore and the tissue, or by bonding the material of the core to theadhesive zone combined with bonding the adhesive zone to the surroundingtissue (FIG. 2). Mechanical bonds can be formed that interlock the corewith the tissue. Alternatively, pressure can be maintained on thecore/tissue interface (FIG. 3).

Cross-Linking.

The formation or attachment of the adhesive zone can be enhanced by theuse of other methods or agents, such as methods or agents thatcross-link the adhesive phase together, or that cross-link the adhesivephase to the tissue, or both. The cross-linking may be by chemicalmeans, such as glutaraldehyde or alcohol, or by physical means, such asheat, ultraviolet (UV) light, dehydrothermal treatment, or lasertreatment. Physical cross-linking methods avoid the release of toxicby-products. Dehydrothermal cross-linking is achieved through drasticdehydration which forms interchain peptide bonds. Ultravioletirradiation is believed to form cross-links between free radicals whichare formed during irradiation.

The cross-linker may be added as an agent (such as a cross-linkingprotein) or performed in situ. The cross-linking may be between thecollagen fibers or may be between other tissue proteins orglycosaminoglycans.

Cross-linking of collagen-based scaffolds affects the strength,biocompatibility, resorption rate, and antigenicity of thesebiomaterials (Torres, Effects Of Modulus Of Elasticity Of CollagenSponges On Their Cell-Mediated Contraction In Vitro (M.S. ThesisMassachusetts Institute of Technology, 1998)(on file with the MITLibrary); Troxel, Delay of skin wound contraction by porous collagen-GAGmatrices (Ph.D. Thesis Massachusetts Institute of Technology, 1994)(onfile with the MIT Library); Weadock et al., 29 J. Biomed. Mater. Res.1373-1379 (1995)).

Cross-linking can be performed using chemicals, such as glutaraldehydeor alcohol, or physical methods, such as ultraviolet light ordehydrothermal treatment. The degree to which the properties of thescaffold are affected is dependent upon the method and degree ofcross-linking. Cross-linking with glutaraldehyde has been widely used toalter the strength and degradation rate of collagen-based biomaterialsscaffolds (Kato & Silver, 11 Biomaterials 169-175 (1990), Torres,Effects Of Modulus Of Elasticity Of Collagen Sponges On TheirCell-Mediated Contraction In Vitro (M.S. Thesis Massachusetts Instituteof Technology, 1998)(on file with the MIT Library); Troxel, Delay OfSkin Wound Contraction By Porous Collagen-GAG Matrices (Ph.D. ThesisMassachusetts Institute of Technology, 1994)(on file with the MITLibrary), and glutaraldehyde-cross-linked collagen products arecommercially available for implant use in urologic and plastic surgeryapplications.

Use of physical cross-linking methods, including dehydrothermal (DHT)treatment and ultraviolet (UV) irradiation, is preferred to the use ofglutaraldehyde for cross-linking. Cross-linking by DHT is achievedthrough drastic dehydration which forms interchain peptide bonds. UVirradiation is believed to form cross-links between free radicals whichare formed during irradiation.

The nonlinear relationship between stress and strain for scaffoldscross-linked using glutaraldehyde, dehydrothermal treatment, ultravioletlight irradiation and ethanol treatment has demonstrated higherstiffness in the ethanol and ultraviolet groups, lowest stiffness in thedehydrothermal cross-linked groups, with the stiffness of theglutaraldehyde group in between (Torres, Effects Of Modulus OfElasticity Of Collagen Sponges On Their Cell-Mediated Contraction InVitro (M.S. Thesis Massachusetts Institute of Technology, 1998)(on filewith the MIT Library)). Torres seeded collagen-based scaffolds with calftenocytes and demonstrated a statistically significant increased rate ofcalf tenocyte cell proliferation in the glutaraldehyde and ethanolcross-linked scaffolds when compared with the dehydrothermalcross-linked group at 14 and 21 days post-seeding. Additional length ofcross-linking in glutaraldehyde lead to increasing stiffness of thecollagen scaffold, with values approaching that seen in the ultravioletand ethanol groups. The ultraviolet cross-linked group demonstrated astatistically significant increase over the dehydrothermal group at 21days, but not at 14 days post-seeding. This result suggests an influenceof cross-linking method with fibroblast proliferation within thecollagen-based scaffold.

Method of Use.

The methods of the invention may be used to treat injuries to theanterior cruciate ligament, the meniscus, labrum, cartilage, and othertissues exposed to synovial fluid after injury.

The intra-articular scaffold is designed for use with arthroscopicequipment. The scaffold is compressible to allow introduction througharthroscopic portals and equipment. The scaffold can also be pre-treatedin antibiotic solution prior to implantation.

For methods involving a collagen-based scaffold, the affected extremityis prepared and draped in the standard sterile fashion. A tourniquet maybe used if indicated. Standard arthroscopy equipment may be used. Afterdiagnostic arthroscopy is performed, and the intra-articular lesionidentified and defined, the tissue ends are pretreated, eithermechanically or chemically, and the scaffold introduced into the tissuedefect. The scaffold is then bonded to the surrounding tissue bycreating chemical or mechanical bonds between the tissue proteins andthe scaffold adhesive zone. This can be done by the addition of achemical agent or a physical agent such ultraviolet light, a laser, orheat. The scaffold may be reinforced by placement of sutures or clips.The arthroscopic portals can be closed and a sterile dressing placed.The post-operative rehabilitation is dependent on the joint affected,the type and size of lesion treated, and the tissue involved.

For methods involving the meniscal glue or tissue-adhesive composition,a diagnostic arthroscopy is performed and the lesion defined. The kneemay be drained of arthroscopic fluid and the glue inserted into the tearunder wet or dry conditions, depending on the composition of the glue.The glue is bonded to the surrounding injured tissue and, when thedesired bonding has been achieved, the knee is refilled witharthroscopic fluid and irrigated. The arthroscopic portals are closedand a sterile dressing applied. The patient is kept in a hinged kneebrace post-operatively, with the degree of flexion allowed dependent onthe location and size of the meniscal tear.

The details of one or more embodiments of the invention have been setforth in the accompanying description above. Although any methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of the present invention, the preferred methodsand materials have been described. Other features, objects, andadvantages of the invention will be apparent from the description andfrom the claims. In the specification and the appended claims, thesingular forms include plural referents unless the context clearlydictates otherwise. Unless defined otherwise, all technical andscientific terms used herein have the same meaning as commonlyunderstood by one of ordinary skill in the art to which this inventionbelongs. All patents and publications cited in this specification areincorporated by reference.

The following EXAMPLES are presented to more fully illustrate thepreferred embodiments of the invention. These EXAMPLES should in no waybe construed as limiting the scope of the invention, as defined only bythe appended claims.

Example 1 Fibroblast Distribution in the Anteromedial Bundle of theHuman Anterior Cruciate Ligament

The purpose of this EXAMPLE is to confirm the presence of cellsexpressing a contractile actin isoform alpha-smooth muscle actin (α-sm;SMA), in the intact human anterior cruciate ligament, as shown by Murray& Spector, 17(1) J. Orthop. Res. 18-27 (1999). Actin is a majorcytoskeletal protein associated with cell motility, secretion,phagocytosis, and cytokinesis. Actin is expressed in mammals as sixisoforms which are coded by different genes and differ in their aminoacid sequence. Two of the isoforms (β and γ) are found in practicallyall cells, while the other four (α's) are thought to representdifferentiation markers of muscle cells. The α-sm actin isoform isassociated with the contractile phase of healing in several connectivetissues, including dermis, cornea, tendon and medial collateralligament. This isoform has also been associated with cell migration byYamanaka & Rennard, 93(4) Clin. Sci. 355-62 (1997).

The anterior cruciate ligament is a complex tissue composed ofstructural proteins, proteoglycans, and cells. The histology of thehuman anterior cruciate ligament is characterized by the specificdistribution and density of the fibroblast phenotype as well as by theunique organization of the structural proteins. Three histologicallydifferent zones were found to be present along the anteromedial bundlefrom the femoral to the tibial attachment. Two of the zones (thefusiform and ovoid) were located in the proximal ⅓ of the bundle. Thethird zone (the spheroid) occupied the distal ⅓ of the bundle fascicles.

The fusiform cell zone had a high number density of longitudinallyoriented cells with a fusiform-shaped nucleus, longitudinal bloodvessels, and high crimp length. The cytoplasm of the cells in thefusiform zone were intimately attached to the extracellular collagen andfollowed the crimp waveform of the fibers. Fusiform cells stainedpositively for the α-sm actin isoform in the fusiform zone, particularlyat areas of crimp disruption.

The ovoid cell zone had a high number density of cells with anovoid-shaped nucleus, longitudinal vessels, and a high crimp length.Ovoid cells stained positively for the α-sm actin isoform in the ovoidcell zone.

The spheroid cell zone had a low density of spheroid cells, few bloodvessels, and short crimp length. Cells were found within and amongfascicles, as well as within lacunae. In selected areas, as many as 50%of the cells in this region stained positively for the α-sm actinisoform. These findings demonstrated the uniformity of cell numberdensity and morphology in the distal β of the anteromedial bundle of thehuman anterior cruciate ligament, and thus a region for transectionwhich would provide the most consistent starting cell density andnuclear morphology.

In summary, cells expressing the α-sm actin isoform are present in theintact human anterior cruciate ligament, in cells with variousmorphologies, and predominantly in cells located at areas of crimpdisruption.

The presence of α-sm actin positive, potentially contractile, cells inthe ruptured human anterior cruciate ligament may provide one possibleexplanation for the retraction of ligament remnants seen after completerupture. Down-regulation of the myofibroblast phenotype may be useful inpreventing premature ligament retraction, while up-regulation may beuseful in self-tensioning of the healed ligament during the remodelingphase. Quantifying the degree of expression of the contractile actin andthe effect of scaffold cross-linking and growth factors on thisexpression is a first step towards understanding possible regulationmechanisms.

Example 2 Fibroblast Migration into the Anteromedial Bundle of the HumanAnterior Cruciate Ligament In Vitro

The purpose of this EXAMPLE was to confirm that human ligamentfibroblasts can migrate into collagen-glycosaminoglycan copolymers invitro.

Methods.

Fifteen intact anterior cruciate ligaments were obtained from total kneearthroplasty patients, ages 54 to 82 years. Four of the ligaments wereused solely for histology and immunohistochemistry. The remainingligaments were sectioned into fascicles that were divided transverselyin the midsubstance to make explants. The highly porouscollagen-glycosaminoglycan matrix, composed of type 1 bovine hidecollagen and chondroitin-6-sulfate, was prepared by freeze-drying thecollagen-glycosaminoglycan dispension as described by Murray & Spector,in 45^(th) Annual Meeting, Orthopaedic Research Society, Anaheim, Calif.(1999). The average pore size of the collagen-glycosaminoglycan scaffoldwas 100 μm. Sample of the collagen-glycosaminoglycan matrix wassandwiched between 2 explants and the construct was stabilized bysuturing the explants to silicone tubing (4 mm i.d.). The constructswere cultured in media containing Dulbecco's DMEM/F12 with 10% fetalbovine serum, 2% penicillin streptomycin, 1% amphotericin B, 1%L-glutamine and 2% ascorbic acid. Samples were fixed in formalin afterone to six weeks, embedded in paraffin, sectioned, and stained withhematoxylin and eosin. Immunohistochemistry using monoclonal antibodiesto detect α-sm actin was also performed. Cell counts were taken at theedge of the scaffold for a cell density measure and the furthestdistance traveled from the tissue/scaffold interface recorded for eachsample.

Results.

After 1 week in culture, fibroblasts in the explants began to displaychanges in morphology, with cells in the periphery becoming rounder. Nocells were seen in the collagen-glycosaminoglycan scaffold. By 2 weeks,disruption of the ligament architecture at the edges of the fasciclecould be observed, along with an increase in cell density at theperiphery of the explants. In 2 of the 6 samples for this time period,cells had migrated into the collagen-glycosaminoglycan scaffold. By 4weeks, further disruption of the normal ligament architecture was noted,as well as additional increases in cell density at the periphery of theexplant. Four of the 6 samples for this time period showed migration ofthe fibroblasts into the scaffold to a distance of 0.1 to 2 mm. The 2remaining samples were from ligaments which had displayed migration intothe scaffold at 2 and 3 weeks. In these samples, the matrix hadcontracted and been resorted to the point that no material wasretrievable. At 5 and 6 weeks, scaffolds that had not yet significantlycontracted demonstrated increasing cell density. There did not appear tobe a correlation between migration kinetics and patient age.

Anterior cruciate ligament tissue examined immediately after theretrieval demonstrated wide variability in the percentage of cells whichstained positive for α-sm actin. In general, a greater percentage ofsuch cells were found in the midsubstance of the fascicles. With time inculture, the explanted tissue gradually developed a higher percentage ofpositive cells at the periphery of the explant. The areas displaying thegreatest number of positive cells appeared to correspond to the areas ofdisrupted ligament architecture. All cells that migrated into thecollagen-glycosaminoglycan scaffold stained positive for α-sm actin.

Discussion.

This EXAMPLE shows the potential for human anterior cruciate ligamentfibroblasts to migrate from their native extracellular matrix intocollagen-glycosaminoglycan scaffolds that may ultimately be used asimplants to facilitate ligament regeneration.

Example 3 The Migration of Human Anterior Cruciate Ligament Fibroblastsinto Porous Collagen-GAG Matrices In Vitro

This EXAMPLE was designed to determine if fibroblasts intrinsic to thehuman anterior cruciate ligament were capable of migrating from theirnative extracellular matrix onto an adjacent provisional scaffold invitro. Another objective was to determine whether any of the cells whichsuccessfully migrated into the scaffold expressed the contractile actinisoform, α-sm actin, associated with wound contraction in other tissues.This EXAMPLE demonstrates that the cells intrinsic to the human anteriorcruciate ligament are able to migrate into a collagen-glycosaminoglycanscaffold, bridging a gap between transected fascicles in vitro.

Explants of human anterior cruciate ligament are useful as the source ofcells for migration testing, because the explants provide a knowndistribution of cells within an extracellular matrix carrier. Thus, anycells which are found in the adjacent collagen-glycosaminoglycanscaffold during the test must have migrated there, as fluid flow duringcell seeding is avoided. This method also avoids possible modificationof cell phenotype which may occur during cell isolation, expansion in2-D culture, and seeding of scaffolds.

As a result of cell migration and proliferation, areas in the scaffoldcontained cell number densities similar to that seen in the humananterior cruciate ligament in vivo. No extracellular matrix or tissuedeposition was seen in the gap between directly apposed transected endsof the anterior cruciate ligament explant cultured without an interposedcollagen-glycosaminoglycan scaffold. Both thefascicle-collagen-glycosaminoglycan-fascicle constructs and thefascicle-fascicle explants displayed minimal adherence after 6 weeks inculture. Any disruption in the contact area between explant andscaffold, even as small a gap as 50 microns, was noted to prevent cellmigration from the explant to the collagen-glycosaminoglycan scaffold atthe area of loss of contact. All cells which migrated into thecollagen-glycosaminoglycan scaffold at early time periods were found toexpress the α-sm actin isoform.

This EXAMPLE demonstrates that cells that migrate into and proliferatewithin the collagen-glycosaminoglycan matrix have contractile potentialas reflected in their expression of the α-sm actin isoform. Moreover,this EXAMPLE demonstrates the potential of cells intrinsic to the humananterior cruciate ligament to migrate into collagen-glycosaminoglycanscaffolds.

Methods.

Six intact anterior cruciate ligaments were obtained from 6 womenundergoing total knee arthroplasty, ages 40 to 78, with a mean age of 58years. Seven fascicles between 1 and 5 mm in diameter were dissectedfrom each ligament. One fascicle from each ligament was allocated forhistology. The remaining 36 fascicles were transected in the middle aand a 1 mm thick section of the midsubstance was taken from the divisionsite for 2-D explant culture (FIG. 4). The two remaining segments ofeach fascicle were then used to form the 3-D test(fascicle-scaffold-fascicle) and control (fascicle-fascicle) constructs(see, below). The middle third of the fascicle was used as the area ofinvestigation because previous histologic evaluation of the anteriorcruciate ligament fascicles revealed that this region had the mostconsistent cell morphology and density.

Explant Culture on a 2-D Surface.

The 36 1-mm thick samples from the midsection of all fascicles werecultured in 35 mm diameter dishes (Corning #430343, 6 well plates,Cambridge, Mass.) containing 1 cc of media comprised of Dulbecco'sDMEM/F12 with 10% fetal bovine serum, 2% penicillin streptomycin, 1%amphotericin B, 1% L-glutamine and 2% ascorbic acid. One of thetransversely cut surfaces was placed against the culture dish. Becauseof the variation in fascicular diameter, the explant area in contactwith the culture dish ranged from 1 mm² to 20 mm². Media were changed 3×a week. Outgrowth from the explant biopsies was recorded every 3 days asthe surface area covered by contiguous fibroblasts. The area ofoutgrowth was measured using an inverted microscope and a transparentgrid sheet. The number of squares covered by the contiguous cells wascounted and the corresponding area determined. The effective radius ofoutgrowth was calculated by assuming a circular area of contiguouscells. The rate of outgrowth was then calculated by plotting the averageeffective radius of outgrowth as a function of time from the firstobserved outgrowth, and the slope from the linear regression analysiswas used as the rate of outgrowth. Twenty-four of the 33 samplesdemonstrated contiguous cell growth for at least 2 consecutive timeperiods prior to termination of the culture and were included in thecalculation of the average rate. All explanted tissue and fibroblasts onthe culture wells were fixed in formalin after 4 weeks in culture.

Collagen-Glycosaminoglycan Scaffold.

The porous collagen-glycosaminoglycan scaffold used in this EXAMPLE hasbeen used successfully in regeneration of dermis (Yannas, in CollagenVol III: Biotechnology, Nimni, ed., p. 87-115 (CRC Press, Boca Raton,Fla., 1989)) and peripheral nerve (Chamberlain, Long Term Functional AndMorphological Evaluation Of Peripheral Nerves Regenerated ThroughDegradable Collagen Implants (M.S. Thesis Massachusetts Institute ofTechnology, 1998)(on file with the MIT Library)). The 3-D culturesubstrate was a highly porous collagen-glycosaminoglycan matrix,composed of type I bovine tendon collagen (Integra Life Sciences, Inc.,Plainsboro, N.J.) and chondroitin-6-sulfate (Sigma Chemical, St. Louis,Mo.). The scaffold was prepared by freeze-drying thecollagen-glycosaminoglycan dispersion under specific freezing conditionsdescribed by Yannas et al, 8 Trans. Soc. Biomater. 146 (1985) to form atube with pore channels preferentially oriented longitudinally. Theaverage pore size of the collagen-glycosaminoglycan scaffoldmanufactured in this manner has previously been reported by Louie,Effect Of A Porous Collagen-Glycosaminoglycan Copolymer On Early TendonHealing In A Novel Animal Model (Ph.D. Thesis Massachusetts Institute ofTechnology, 1997)(on file with the MIT Library) as 100 μm.

Fascicular Collagen-Glycosaminoglycan Scaffold Constructs.

The 6 fascicles from each of the 6 patients were divided into test(fascicle-scaffold-fascicle) and control (fascicle-fascicle) groups.This yielded one test and one control construct per patient forexamination after 2 weeks, 4 weeks, and 6 weeks in culture, providing 6test and 6 control constructs at each of the 3 time points.

The 18 test constructs were made by suturing each of the 2 fasciclelengths to an open channel cut from silicon tubing such that a 3-mm gapseparated the transected ends. A 5-mm length ofcollagen-glycosaminoglycan scaffold (see, below) was compressed into thegap (FIG. 5). The 18 control constructs were made by reapposing thetransected ends and then securing the fascicles to similar open channels(FIG. 5). All of the 36 fascicle constructs were cultured in mediacontaining Dulbecco's DMEMI F12 with 10% fetal bovine serum, 2%penicillin streptomycin, 1% amphotericin B, 1% L-glutamine and 2%ascorbic acid. Media were changed 3× a week.

Histologic Evaluation.

One test and one control construct from each patient (n=6) were fixed informalin after 2, 4 and 6 weeks in culture. After formalin fixation forat least 72 hr, samples were dehydrated through graded solutions ofethanol and embedded in paraffin. Microtomed sections were cut at 6 μmthickness. Hematoxylin and eosin staining and immunohistochemicalstaining for α-sm actin (see, below) were performed for each construct.Sections were examined using a Vanox-T AH-2 microscope (Olympus, Tokyo,Japan) with normal and polarized light.

For each construct, eleven points along the length were counted for cellnumber density. For each region, 3 areas of 250×400 μm were analyzed.Within each of the two fascicles, cell number density was counted at theedge of the fascicle, 1 mm from the edge and 2 mm into the bulk of thefascicle. The two values for each position (one in each fascicle) wereaveraged to obtain the values for the construct (n=6). Within thecollagen-glycosaminoglycan scaffold, cell number density was counted ateach edge in contact with the fascicle, as well as 1 and 2 mm from eachedge of the scaffold. The 2 values for each position (from each contactedge) were averaged to obtain the values for the construct (n=6). Theaverage value for cell number at each position was multiplied by 10 toobtain the number of cells/mm² (see, FIG. 19). The fascicular tissue andcollagen-glycosaminoglycan scaffolding were examined using polarizedlight to determine the degree of crimp and collagen alignment.

Immunohistochemistry.

The expression of α-sm actin was determined using a monoclonal antibody.For the 3-D culture specimens, deparaffinized, hydrated slides weredigested with 0.1% trypsin (Sigma Chemical, St. Louis, Mo., USA) for 20minutes (min). Endogenous peroxidase was quenched with 3% hydrogenperoxide for 5 min. Nonspecific sites were blocked using 20% goat serumfor 30 min. The sections were then incubated with the mouse anti-α-smactin monoclonal antibody (Sigma Chemical, St. Louis, Mo., USA) for 1 hrat room temperature. Negative controls were incubated with mouse serumdiluted to an identical protein content. The sections were thenincubated with biotinylated goat anti-mouse IgG secondary antibody for30 min followed by 30 min of incubation with affinity purified avidin.The labeling was developed using the AEC chromagen kit (Sigma Chemical,St. Louis, Mo.) for ten min. Counterstaining with Mayer's hematoxylinfor 20 min was followed by a 20 min tap water wash and coverslippingwith warmed glycerol gelatin.

Histology of the Ligament Fascicles.

The histology of the fascicles from each of the 6 patients was asfollows: The proximal ⅓ was populated predominantly by fusiform andovoid cells in relatively high density, and the distal ⅔ was populatedby a lower density of spheroid cells. The level of transection used toproduce the fascicle constructs was in the spheroid cell region, withsimilar cell morphologies and an average cell number density of 498±34cells/mm² (n=6). α-sm actin immunohistochemistry of the transectedregion showed positive staining in 8.3±3.0% of fibroblasts notassociated with blood vessels.

Changes in the Fascicular Tissue with Time in Culture.

With time in culture, changes in the cell distribution and extracellularmatrix organization of the anterior cruciate ligament tissue in the 36test and control fascicular constructs were observed. Fusiform, ovoidand spheroid nuclear cell morphologies could be observed in the bulk ofthe cultured fascicles. Time in culture was noted to have astatistically significant effect on the cell number density at eachlocation (i.e., at the edge and at 1 and 2 mm into the bulk of thefascicle; one-way ANOVA, p<0.001). The number density of cells at theedge of the explants decreased to 120±29 cells/mm² at 2 weeks and to101±28 cells/mm² at six weeks, both of which were different from thecell number density at retrieval, 498±34 cells/mm², as noted above(paired t-test, p<0.001). The number of cells within the bulk of thefascicle decreased as well, to 58±21 cells/mm² at 2 weeks and 19±20cells/mm² at six weeks, again, both densities were significantlydifferent from that at retrieval (paired t-test, p<0.0001).

At 2 and 4 weeks, the percentage of cells staining positive for α-smactin increased to 30±8% at the edge of the fascicles compared with the8.3±3.0% before culture (paired t-test, p=0.06); none of the cells 2 mminto the bulk of the fascicle stained positive for α-sm actin. Thepercentage of cells expressing the α-sm actin isoform at the edge of thefascicle decreased with time in culture to 6±4% at week 6, a value notstatistically significantly different from that before culture (pairedt-test, p>0.30). The percentage of cells staining positive for α-smactin remained low in the bulk of the fascicle, with 2±2% of cellsstaining positive at 6 weeks.

The extracellular matrix of the explant exhibited disruption of thestructural organization with time in culture. Loss of crimp andfascicular alignment was severe enough at the 2 week time point toprohibit any measure of crimp length or degree of organization. The nearuniaxial alignment and crimp of the collagen fibers was lost and thetissue assumed a looser appearance.

2-D Culture Outgrowth.

The outgrowth of cells onto the 2-D culture dishes was observed to occuras early as 6 days and as late as 19 days, with outgrowth first detectedafter an average of 10±3 days. The time of onset or rate of outgrowthwas not found to correlate with explant size. Linear regression analysisof the plot of effective outgrowth radius versus time for all explantsthat demonstrated contiguous outgrowth had a coefficient ofdetermination of 0.98. The average rate of outgrowth, represented by theslope of this plot, was 0.25 mm/day (FIG. 6).

3-D Culture Outgrowth. The reapposed tissue ends of the 18 control(fascicle-fascicle) constructs had no adherence to each other even aftersix weeks in culture; as soon as the retaining sutures were removed, thefascicle ends separated. Histologically, no matrix deposition was seenbetween or adjacent to the transected fascicle ends, although increasesin cell density at the periphery of the fascicles were noted.

In the constructs with interposed collagen-glycosaminoglycanscaffolding, fibroblasts were noted to migrate from the human anteriorcruciate ligament fascicles into the scaffolds at the earliest timepoint (2 weeks). Migration into the scaffold was seen in 5 of 6constructs at 2 weeks, 5 of 6 constructs at 4 weeks, and in all 5 of the6-week constructs. While the average cell number density in the fascicledecreased with time, the average cell number density in the scaffoldincreased with time in culture (FIG. 7). Initially, cells were notedpredominantly at the edge of the scaffold. With time, the average cellnumber density at the edge of the scaffold increased from 57±22cells/mm² at 2 weeks and to 120±41 cells/mm² at six weeks. While thiswas a 2-fold increase, it was not found to be statistically significant(p=0.15) owing to the large coefficient of variation. The average cellnumber density 1 mm within the scaffold also increased from 6±2cells/mm² at 2 weeks to 25±10 cells/mm² at 4 weeks and to 47±37cells/mm² at 6 weeks. Again, owing to the large variation, theseincreases were not statistically significant (p=0.15), despite beingincreases of several-fold. While there was a consistent increase in themean value of the cell number density with time at the various distancesfrom the scaffold/fascicle interface, two way ANOVA showed nosignificant effect of time in culture on cell number density at eachlocation (p=0.10), but did reveal a significant effect of location oncell number density (p<0.001). The maximum cell number density offibroblasts in the scaffold increased with time from 123±45 cells/mm² at2 weeks to 336±75 cells/mm² at six weeks, a difference which wasstatistically significant (Student t test, p=0.05). The relationshipbetween maximum cell number density and time was well modeled by alinear regression, with a coefficient of determination of 0.96 (FIG. 8).Cells migrating into the collagen-glycosaminoglycan scaffolddemonstrated all of the three previously described ligament fibroblastmorphologies: (1) fusiform or spindle-shaped, (2) ovoid, and (3)spheroid. The average migration distance at the 2-week time period was475 micrometers. At the 4-week time point, cells had migrated as far as1.5 mm toward the center of the scaffold. In areas where a gap greaterthan 50 microns was present between the explant andcollagen-glycosaminoglycan scaffold, no cell migration into the scaffoldwas seen.

All cells which migrated into the collagen-glycosaminoglycan sponge werefound to be positive for α-sm actin at the 2-week period. These cellsdemonstrated both unipolar and bipolar staining with the chromagenappearing prominently in the cytoplasm on only one side or on both sidesof the nucleus. The percentage of cells staining positive decreased withtime, with the edge of the scaffold having only 66±9% of cells stainingpositive at the six-week time point, and the bulk of the scaffoldcontaining 95±4% positively staining cells. Particularly, cells locatedin areas of high cell density were noted to no longer stain positive.

No remarkable degradation of the scaffold was found during the timecourse of the EXAMPLE, although the average pore diameter was notedqualitatively to decrease with time in culture.

Discussion.

This EXAMPLE demonstrates that the cells intrinsic to the human anteriorcruciate ligament were able to migrate into the gap between transectedfascicles, eventually attaining selected areas with cell numberdensities similar to that seen in the human anterior cruciate ligamentin vivo, if a provisional scaffold was provided. No extracellular matrixformation was seen between transected ends directly apposed withoutprovisional scaffold. A gap between the explant and scaffold, even, assmall as 50 μm, prevented cell migration to the scaffold at the site ofloss of contact. Cells with all three previously described ligamentfibroblast morphologies—fusiform, ovoid and spheroid—were noted tomigrate into the scaffold. The cell density within the scaffold andmaximum migration distance increased with time. These results show thatcells intrinsic to the human anterior cruciate ligament are capable ofmigrating from their native extracellular matrix onto an adjacentcollagen-glycosaminoglycan scaffold, if contact between the scaffold andexplant is maintained, and do so in increasing numbers with time inculture.

Outgrowth from explants likely has two components—migration andproliferation. Previous results assumed minimal contribution from theproliferation component and reported outgrowth rates as migration rates(Geiger et al., 30(3) Connect Tissue Res. 215-224 (1994)); the migrationrate from rabbit anterior cruciate ligament explants was 0.48 mm/day.Using this same approach, the migration rate from human anteriorcruciate ligament explants In this EXAMPLE is 0.25 mm/day. Previousstudies did not report the cell number density of the explants (seealso, Deie et al., 66(1) Acta Orthop. Scand. 28-32 (1995)), so onecannot predict whether differences in reported results are due tospecies differences or to differences in the cell number density orphenotype.

This EXAMPLE demonstrates the chronology of expression of this phenotypein explants of ligament tissue in culture, as well as in cells whichsuccessfully migrate onto a 3-D scaffold. The percentage of α-smactin-positive cells increases at the periphery of the explants from 8to 30% after 2 weeks in culture. All ligament cells which migrated intothe collagen-glycosaminoglycan matrix at 2 weeks contained α-sm actin,suggesting a role for this contractile actin isoform in cell migration.Moreover, most of these cells displayed a unipolar distribution of thecontractile actin isoform. While the histological plane through thesample may have resulted in an asymmetric appearance of α-sm actin, itis unlikely that this was the sole cause of the appearance of unipolarstaining. This unipolar distribution of the contractile protein may beassociated with asymmetric contraction of the cytoplasm to facilitatecell movement.

Cells in the scaffold displayed bipolar, as well as unipolar,distribution of α-sm actin. Cells that attached to two walls of a poreof the scaffold often displayed the bipolar distribution. Bipolarexpression of the contractile protein may lead to symmetric contractionof the cell cytoplasm and contracture of the matrix to which the cell isattached. This may have been responsible for the qualitative observationof a decrease in pore diameter of the collagen-glycosaminoglycan matrixwith time in culture.

The anterior cruciate ligaments used in this EXAMPLE were all intactprior to resection, which suggests that the cells intrinsic to theligament were able to maintain tissue structure.

This EXAMPLE shows the potential of human anterior cruciate ligamentfibroblasts to migrate from their native extracellular matrix intocollagen-glycosaminoglycan scaffolds that may ultimately be investigatedas implants to facilitate ligament healing. The EXAMPLE allows for theanalysis of the migration of fibroblasts out of human tissues directlyonto a porous 3-D scaffold.

Example 4 Scaffold Optimization for Healing of the Ruptured HumanAnterior Cruciate Ligament

The purpose of this EXAMPLE is to demonstrate the process offibroblast-mediated tissue regeneration, to determine the effect ofcross-linking of a collagen-based scaffold on (a) the rate of fibroblastmigration; (b) the rate of fibroblast proliferation; (c) expression of acontractile actin; and (d) the rate of type I collagen synthesis byfibroblasts in the collagen-based scaffold. This EXAMPLE is alsointended to determine the effect of addition of selected growth factorson these same outcome variables. The results of this EXAMPLE can be usedto determine how specific alterations in scaffold cross-linking and theaddition of specific growth factors alter the fibroinductive propertiesof a collagen-based scaffold. For the purposes of this EXAMPLE, thefibroinductive potential of the scaffold is defined as its ability topromote fibroblast infiltration, proliferation and type I collagensynthesis.

Two scientific rationales relate to the purposes listed above:

The method and degree of cross-linking alter the rate of fibroblastmigration from an anterior cruciate ligament explant into acollagen-based scaffold as well as the rate of fibroblast proliferation,expression of a contractile actin, and type I collagen synthesis withinthe scaffold. The bases for these rationales are results which havedemonstrated (a) alteration in fibroblast proliferation rates andexpression of the contractile actin isoform after fibroblast seeding ofcross-linked scaffolds; and (b) differences in rates of collagensynthesis by chondrocytes seeded into type I and type II collagen-basedscaffolds. Solubilized fragments of collagen resulting from thedegradation of the collagen-based scaffold may affect cell metabolism.These fragments may form at different rates for different cross-linkingmethods. Therefore, the fibroinductive properties of the collagen-basedscaffold may be regulated by the choice of cross-linking method.

The addition of growth factors to the collagen-glycosaminoglycanscaffold alters (a) the rates of fibroblast migration from an anteriorcruciate ligament explant to a collagen-based scaffold; (b) the rates offibroblast proliferation; (c) the expression of a contractile actin; and(d) the type I collagen synthesis within the scaffold. The bases forthis rationale are (a) the alteration in fibroblast migration rates onto2-D surfaces, (b) synthesis of type I collagen in vitro when growthfactors are added to the culture media, and (c) alterations in rates ofincisional wound healing. The effects of 4 different growth factors and4 collagen-based substrates on features associated with the repairprocesses in connective tissues which successfully heal are assayed for:(1) fibroblast migration; (2) proliferation; and (3) type I, II and IIIcollagen synthesis. For the purposes of this EXAMPLE, these are referredto as fibroinductive properties.

Assay Design.

Explants from human anterior cruciate ligaments are placed into culturewith a type I collagen-glycosaminoglycan scaffold in a construct (see,EXAMPLE 3). Migration rates of cells from the explant into thecollagen-glycosaminoglycan scaffold are measured at 1, 2, and 4 weeks.Three constructs for each of the 4 types of cross-linking are requiredfor each time point: (1) one explant/scaffold specimen for histology forthe migration calculations and α-sm actin immunohistochemistry; (2) onespecimen for the DNA assay for proliferation, and (3) a third specimenfor SDS-PAGE analysis for type I collagen synthesis. One additionalconstruct is fixed immediately for histology. Thus, 10 explant/scaffoldconstructs are used for each type of cross-linked scaffold or growthfactor tested. The power calculation for sample size for the number ofpatients to include is based on detecting a 30% difference in the meanvalues of the outcome variables. Assuming a 20% standard deviation, apower of 0.80 (β=0.20), and a level of significance of α=0.05, n=6patients are required. For the cross-linking phase, human anteriorcruciate ligament tissue are obtained from 6 patients and 10explant/scaffold constructs made for each of the four types ofcross-linked collagen (a total of 40 constructs per patient). For thegrowth factor phase, human anterior cruciate ligament tissue areobtained from 6 additional patients and 10 explant/scaffold constructsmade for each of the four types of cross-linked collagen (a total of 40constructs/patient).

Materials.

The test constructs used in this EXAMPLE are explants of human tissueplaced into culture directly onto 3-D fibrous collagen-glycosaminoglycanscaffolds (see, EXAMPLE 3). Human anterior cruciate ligament explantsare obtained from patients undergoing total knee arthroplasty.

This construct allows for the analysis of the migration of fibroblastsout of human tissues directly onto a 3 D fibrous scaffold in acontrolled in vitro environment and obviates several confoundingfactors, such as modulation of cell phenotype, which may occur duringcell extraction or 2-D cell culture. This construct also allows forinvestigation of human fibroblasts and tissue, thus avoidinginterspecies variability. Careful control of growth factor concentrationand substrate selection are also possible with this in vitro model.

Preparation of the Collagen-Based Scaffold.

Type I collagen from bovine tendon is combined with chondroitin 6sulfate from shark cartilage to form a co-precipitate slurry. The slurryis lyophilized in a freeze drier and minimally cross-linked withdehydrothermal treatment for 24 hr at 105° C. and 30 mtorr.

Cross-Linking.

All of the 3-D collagen-glycosaminoglycan scaffolds are minimallycross-linked using dehydrothermal treatment at 105° C. and 30 mtorr for24 hr. Additional cross-linking is performed for the glutaraldehyde,ultraviolet, and ethanol groups. Glutaraldehyde cross-linking areperformed by rehydrating the collagen-based scaffolds in acetic acid,treating in 0.25% glutaraldehyde for thirty minutes, rinsing and storingin a buffer solution. Ethanol cross-linking is performed by soaking thecollagen scaffolds in 70% ethanol for 10 min, rinsing, and storing inbuffer. Ultraviolet light cross-linking is performed by placing thescaffold 30 cm from an ultraviolet lamp rated at 5.3 W total output,55.5 W/cm² at 1 m. The scaffolds is cross-linked for 12 hr, 6 hr on eachside as previously described by Torres, Effects Of Modulus Of ElasticityOf Collagen Sponges On Their Cell-Mediated Contraction In Vitro (M.S.Thesis Massachusetts Institute of Technology, 1998)(on file with the MITLibrary).

Addition of Growth Factors.

The 4 growth factors are added to the cell culture media inconcentrations based on those previously reported to be successful inthe literature: (1) EGF at 10 ng/ml; (2) bFGF at 0.6 ng/ml; (3) TGF-β at0.6 ng/ml; and (4) PDGF-AB at 10 ng/ml. Each growth factor is addedindividually to the control cell culture media containing DMEM-F12, 0.5%fetal bovine serum, 2% penicillin/streptomypin, 1% amphotericin B, 1%L-glutamine and 25 μg/ml of ascorbic acid.

Culture of Explant/Scaffold Constructs.

For the 3-D tests, explants are placed onto previously prepared 9 mmdiscs of collagen-glycosaminoglycan scaffold. Cell culture media isadded to just cover the scaffold and changed every 3 days. Constructsare sacrificed at 1, 2, and 4 weeks.

Histology for Analysis of Cell Migration.

All specimens for light microscopy, including control fascicles andexplants are fixed in 10% neutral buffered formalin for one week,embedded in paraffin and sectioned into 7 micrometer sections. Sectionsare taken perpendicular to the explant/scaffold interface to allow formigration measurements. Hematoxylin and eosin staining are performed tofacilitate light microscopy examination of cell morphology in bothexplant and scaffold, maximum migration distance into thecollagen-glycosaminoglycan scaffold and maximal number density offibroblasts in the scaffold.

DNA Assay for Cell Proliferation.

Specimens allocated for analysis of DNA content are fluorometrically.Specimens are rinsed in phosphate-buffered saline and the explantseparated from the scaffold. The scaffold is stored at −70° C. Thescaffold is digested in 1 ml of 0.5% papain/buffer solution in a 65° C.water bath. A 200 μl aliquot of the digest is combined with 40 μl ofHoechst dye no. 33258 and evaluated fluorometrically. The results areextrapolated from a standard curve using calf thymus DNA. For one run ofthe DNA assay, a standard curve based on a sample of human ligamentcells are used to estimate the cell number from the DNA measurement.Negative control specimens consisting of the scaffold material alone arealso assayed to assess background from the scaffold.

Additionally, a tritiated thymidine assay can be evaluated. Then, thespecimens used for proliferation can be fixed and serially sectioned,with sections at regular intervals examined for cell number density.Maximum number density is recorded for each specimen type. Associatedhistology is used to estimate the percentage of dead cells.

SDS-PAGE Analysis for the Synthesis of Type I Collagen.

Type I, II and III collagen production is measured using SDS-PAGEtechniques. Specimens allocated for analysis of synthesis of type Icollagen are cultured with tritiated proline for specific time periodsafter selected time in culture. Proline uptake studies is performed forscaffolds from each group. Biochemical determination of collagen typesin both the scaffold and conditioned media is eluted with Triton andassayed by PAGE.

Immunohistochemistry.

Immunohistochemistry is used to determine the distribution of cellsproducing the α-sm actin isoform in both the explanted tissue and thescaffold (see EXAMPLE 3). An additional benefits of this construct isthat serial sections can be stained immunohistochemically for anyprotein for which an antibody is available. Therefore, additionalinvestigation into the expression of the other subtypes of actin, ormembers of the integrin family during cellular migration may beperformed, if time allows.

Transmission Electron Microscopy.

Transmission electron microscopy is used to evaluate morphologicfeatures of the migrating cells, as well changes in the extracellularmatrix. Processing of specimens for transmission electron microscopyanalysis begins with fixation for 6 hr in Kamovsky's fixative, followedby post-fixation with osmium tetraoxide, dehydration through gradedalcohols, infiltration with graded propylene oxide/epon, embedding inepon, ultramicrotomy (70 angstroms) and post-staining with uranylacetate. Characteristics of migrating cells to be examined in the TEMinclude characteristics of cytoplasm (such as the presence of abundantrough endoplasmic reticulum and presence of microfilaments consistentwith α-sm actin) and characteristics of extracellular matrix (such asthe presence of pericellular fine fibrils consistent with new collagenformation).

Analysis.

The principal variables evaluated are the number of cells populating thescaffold, the production of type I, II and III collagen, and theexpression of the contractile actin isoform. The control group are theminimally cross-linked scaffolds with no growth factor addition.Assuming a standard deviation of 30%, to detect a difference betweengroups of 30%, with an “α” of 0.05 and a “β” of 0.1 (i.e., a power of90%) has a sample size of 13 for each group. Therefore, to investigate 4growth factors at 4 time points uses 208 constructs each for thehistology and TEM, DNA testing, and SDS-PAGE analysis, a total of 624constructs. An identical number is required to investigate the 4 methodsof cross-linking.

Example 5 Migration of Cells from Ruptured Human Anterior CruciateLigament Explants into Collagen-GAG Matrices

How does the cellular response to injury affect migration behavior? Theobjective of this EXAMPLE was to evaluate the migration of cells fromexplants from selected zones within ruptured human anterior cruciateligaments into collagen-glycosaminoglycan matrices in vitro. Theproliferation of cells in the matrices and their contractile behaviorwere also assessed.

Methods.

Four ruptured human anterior cruciate ligaments were removed frompatients undergoing reconstructive procedures. The ruptures occurred inthe proximal third of the ligaments. One explant was prepared from eachof three zones in the tibial remnant: the femoral, middle, and tibialzones. The explants were placed on top of 9-mm diametercollagen-glycosaminoglycan matrices and analyzed after 1, 2, 3, and 4weeks (n=4).

The collagen-glycosaminoglycan matrix was prepared by freeze-drying acoprecipitate of type I bovine tendon collagen (Integra Life Science,Plainsboro, N.J.) and shark chondroitin 6-sulfate (Sigma Chem. Co., St.Louis, Mo.). The matrix was cross-linked for 24 hr. using adehydrothermal treatment. The scaffolds had a pore diameter ofapproximately 90 μm.

The diameter of the sponges was measured with time in culture. Matriceswithout explants were cultured under the same conditions as controls.The cell density within the matrices was determined by dividing thenumber of cells evaluated histologically by the area of analysis, andimmunohistochemistry using a monoclonal antibody was performed todetermine the percentage of cells containing a contractile actinisoform, α-smooth muscle actin (α-sm). The results were compared withcells migrating from explants obtained from intact human anteriorcruciate ligament specimens.

Results.

Cells from the explants migrated into, and proliferated within, thecollagen-glycosaminoglycan matrices resulting in an increase in the celldensity in the scaffolds with time (FIG. 9). Two-way ANOVA revealed asignificant effect of the location from which the explant was taken oncell density (p=0.009), but not of time in culture (p=0.11). There wasmore active migration and prolferation of cells from the femoral zone ofthe ruptured anterior cruciate ligaments than from cells from the middleand tibial regions (FIG. 9). The cell density resulting from explantsfrom the femoral zone of the ruptured anterior cruciate ligaments wasgreater than that from intact human anterior cruciate ligament explantsafter 2 (110±38 cells/mm²; mean±SEM) and 4 weeks (170±71).Immunohistochemistry revealed the presence of α-sm in the ligament cellsin the scaffolds. There was a significant decrease in the diameter ofthe matrices with time in culture to approximately 70% of the originaldiameter evidencing the contractile behavior of the α-sm-positive cells.

Discussion.

The results of this EXAMPLE demonstrate that cells in the ruptured humananterior cruciate ligament, particularly in the proximal region near therupture site, have the capability to migrate into, and proliferatewithin, collagen-glycosaminoglycan scaffolds that could ultimately beused as implants to facilitate regeneration of the tissue. Moreover,cells growing out from the ruptured anterior cruciate ligament expressthe gene for a contractile actin isoform. The expression of α-sm inother connective tissue cells contributes to healing through woundclosure. This work provides guidance for strategies for the tissueengineering of the anterior cruciate ligament in vivo.

Example 6 Changes in Human ACL Migration Potential after LigamentRupture

The objective of this EXAMPLE was to determine whether anterior cruciateligament cells would continue to migrate after complete rupture, and todetermine what effect the location of cells in the ruptured humananterior cruciate ligament had on their ability to migrate.

Methods.

Ruptured (n=6) anterior cruciate ligaments were retrieved from patientsundergoing anterior cruciate ligament reconstruction. Explants weretaken from the rupture site and placed in culture with ah collagen-basedscaffold. Explants from ruptured ligaments far from the site of rupture(n=6) and from intact anterior cruciate ligaments (n=10) were also placein culture with the scaffolds and analyzed as control groups. Scaffoldswere analyzed after 2, 3, and 4 weeks in culture to determine thedensity of cells migrating into the scaffold as a function of time.

Results.

Cells were noted to migrate from the anterior cruciate ligament rupturesite into the scaffold at the earliest time point (two weeks). Higherdensities of cells were noted to migrate from explants obtained at thesite of rupture than from explants taken far from the rupture site, orfrom the intact anterior cruciate ligaments (FIG. 10). Two-way ANOVAdemonstrated explant location in the ligament had a significant effecton cell number density in the scaffold for the ruptured ligaments(p<0.0001), but that time in culture did not have a significant effect.Maximum cell number densities in the scaffold (335±200 cells/mm²).

Discussion and Conclusions.

The cells of the ruptured human anterior cruciate ligament are able tomigrate to an adjacent scaffold, and do so at higher rates than cellsfrom the intact ligament. The anterior cruciate ligament cells in thecollagen-glycosaminoglycan scaffold reach cell number densities at somesites similar to those of the intact anterior cruciate ligament. Thus,this EXAMPLE's approach of developing a ligament repair scaffold, or“bridge” which re-connects the ruptured ligament ends is useful infacilitating ligament repair after rupture.

Example 7 Angiogenesis and Fibroblast Proliferation in the HumanAnterior Cruciate Ligament after Complete Rupture

This EXAMPLE was performed to determine if two of the biologic responsesrequired for regeneration of tissue (revascularization and fibroblastproliferation) occur in the human anterior cruciate ligament afterinjury.

Materials and Methods.

Twenty-three ruptured anterior cruciate ligament reminants were obtainedfrom 17 men and 6 women (ages 20 to 46, average 31 years), undergoinganterior cruciate ligament reconstruction. The ruptured ligaments wereobtained between 10 days and 2 years after rupture. Then intactligaments were obtained from 3 men and 7 women (ages 57 to 83, average69 years) undergoing total knee arthroplasty for degenerative jointdisease. The ligaments were fixed in formalin, embedded in paraffin,sectioned longitudinally and stained with hematoxylin and eosin and amonoclonal antibody (Sigma Chemical, St. Louis, Mo.) for alpha-smoothmuscle actin (α-sm). Histomorphometric analysis was performed todetermine cell number density, blood vessel density, nuclear aspectratio and the percentage of α-sm positive, non-vascular cells at 1-2 mmincrements along the length of the ligament section. Blood vesseldensity was determined by measuring the width of the section andcounting the number of vessels crossing that width. Two-way ANOVA wasused to determine the significance of time after injury, distance fromthe site of injury, and patient age on the cell number density, bloodvessel density, nuclear morphometry and α-sm positive staining withinthe ligaments. Bonferroni-Dunn post-hoc testing was used to generatespecific p values between groups.

Results.

No bridging clot or tissue was noted grossly between the femoral andtibial reminants at the time of retrieval for any of the rupturedligaments. Four progressive phases of response were seen in the ligamentreminants with time.

Phase I. Inflammation.

Ligament edema observed grossly and inflammatory cells within the tissuedominated the first three weeks after rupture. Dilated arterioles andintimal hyperplasia were noted. Loss of the regular crimp pattern wasnoted near the site of injury, but maintained 4-6 mm from the site ofinjury.

Phase II. Epiligamentous Regeneration.

Between three and eight weeks after rupture, gradual overgrowth ofepiligamentous tissue with a synovial sheath was noted to form over theruptured end of the ligament remnant. Histologically, this phase wascharacterized by a relatively unchanging blood vessel density and cellnumber density within the remnant.

Phase III. Proliferation.

Between right and twenty weeks after rupture, the proliferative responsein the epiligamentous tissue subsided and a marked increase in cellnumber density and blood vessel density within the ligament remnant wasnoted. Fibroblasts were the predominant cell type. Vascular endothelialcapillary buds were noted to appear at the beginning of this phase, andloops from anastomoses of proximal sprouts began to form a diffusenetwork of immature capillaries within the ligament remnant.

Phase IV. Remodeling and Maturation.

Between one and two years after ligament rupture, remodeling andmaturation of the ligament remnant were seen. The ligament ends weredense and white, with little fatty synovium seen overlying them.Histologically, the fibroblast nuclei were increasingly uniform in shapeand orientation, with the longitudinal axis of the nuclei demonstratingincreasing alignment with the longitudinal axis of the ligament remnant.Decreased cell number density and blood vessel density were seen duringthis phase, to a level similar to that seen in the intact human anteriorcruciate ligaments.

Cell number density in the ligament in the ligament after rupture wasdependent on time after injury and distance from the injury site. Thecell number density within the ligament remnant peaked at 16 to 20 weeks(FIG. 11, p<0.005), and was highest near the site of the injury at alltime points (TABLE 1). Patient age was not found to significantly affectcell number density (p>0.80). Blood vessel density was dependent on timeafter injury, with a peak at 16 to 20 weeks (p<0.003). Age did not havea significant effect on vessel density. Cells straining positive for thecontractile actin isoform, α-sm, were present throughout the intact andruptured anterior cruciate ligaments. Time after injury and age of thepatient were not found to significantly effect the percentage of cellsstraining positive.

TABLE 1 Histomorphometry of the intact ACL and distal remnant of theruptured ACL Ruptured 1 mm 2 mm 4 mm Weeks post-rupture edge from edgefrom edge from edge Intact ACL (n = 10) Cell density (#/mm²) 701 ± 201525 ± 108 539 ± 91  294 ± 37  Vessel density (#/mm)  1.5 ± 0.16 1.2 ±0.2  0.6 ± 0.12 0.24 ± .03  % SMA positive cells 4.7 ± 1.0 7.3 ± 1.710.7 ± 3.0   15 ± 3.9 1 to 6 weeks (n = 6) Cell density (#/mm²) 614 ±249 476 ± 267 420 ± 210 254 ± 48  Vessel density (#/mm)  4 ± 3.3 2.9 ±2.6 5.0 ± 2.9 0.8 ± 0.2 % SMA positive cells 2.3 ± 1.4 1.9 ± 1.1 1.0 ±0.3 0.83 ± 0.31 8 to 12 weeks (n = 5) Cell density (#/mm²) 1541 ± 451 1272 ± 363  956 ± 249 701 ± 162 Vessel density (#/mm) 5.1 ± 3.1 4.0 ±2.6 3.0 ± 2.1 2.2 ± 1.0 % SMA positive cells  1.3 ± 0.76  1.3 ± 0.28 1.1 ± 0.33 0.5 ± 0.3 16 to 20 weeks (n = 6) Cell density (#/mm²) 2244 ±526  1522 ± 285  1037 ± 280  833 ± 312 Vessel density (#/mm) 13.3 ± 4.9 4.0 ± 1.3 5.2 ± 2.0 2.9 ± 1.6 % SMA positive cells 0.6 ± 0.3 0.4 ± 0.20.3 ± 0.2 0.3 ± 0.3 52 to 104 weeks (n = 6) Cell density (#/mm²) 559 ±115 601 ± 204 718 ± 241 590 ± 46  Vessel density (#/mm) 2.1 ± 2.0 1.5 ±1.3 1.2 ± 0.7 1.3 ± 0.6 % SMA positive cells 0.5 ± 0.3 0.2 ± 0.2 0.2 ±0.1 0.5 ± 0.2

Discussion.

The human anterior cruciate ligament undergoes a process ofrevascularization and fibroblast proliferation after complete rupture.The healing response can be described in four phases, with a peak inactivity at 4 to 5 months after rupture. This response is similar tothat seen in other dense, organized, connective tissues which heal, suchas the medial collateral ligament, with two exceptions: (1) the lack ofany tissue bridging the rupture site after injury, and (2) the presenceof an epiligamentous regeneration phase. The results of this EXAMPLE,showing that fibroblast proliferation and angiogenesis occur within thehuman anterior cruciate ligament remnant, are important to thedevelopment of future methods of facilitating anterior cruciate ligamenthealing. Harnessing the neovascularization and cell proliferation, andextending it into the gap between ruptured ligament ends providesguidance for a method of anterior cruciate ligament repair.

Example 8 Outgrowth of Chondrocytes from Human Articular CartilageExplants and Expression of Alpha-Smooth Muscle Actin

The objectives of this EXAMPLE were to investigate the effects ofenzymatic treatment on the potential for cell outgrowth from adult humanarticular cartilage and to determine if α-sm is present in chondrocytesin articular cartilage and in the outgrowing cells.

Material and Methods.

Samples of articular cartilage were obtained from 15 patients undergoingtotal joint arthroplasty for osteoarthrosis. While the specimens wereobtained from patients with joint pathology, areas of cartilage with nogrossly noticeable thinning, fissuring, or fibrillation were selected.Using a dermal punch, cylindrical samples (4.5 mm diameter and 2-3 mmthick), were cut from the specimens. Explants were cultured in 6-wellculture dishes and oriented so that deep zone of the tissue contractedthe culture dish. In the first test, 20 cartilage samples were obtainedfrom each of the 9 patients. Four plugs of cartilage were allocated toone of five groups that received collagenase treatment for 0, 1, 5, 10,or 15 min. The time to cell attachment after outgrowth was determinedand cultures were terminated after 28 days. From 6 of the 9 patients,additional plugs, untreated and treated with collagenase for 15 minutes,were evaluated for α-sm, immediately after treatment, and at 6, 14 and20 days in culture. In the second test, 24 cartilage plugs were obtainedfrom each of 6 additional patients. Four plugs were allocated to 5groups receiving a different enzymatic treatment for 15 min. and a sixthuntreated control group: (a) 380 U/ml clostridial collagenase (0.1%;Sigma Chemical, St. Louis, Mo.); (b) 1100 U/ml hyaluronidase (0.1%;Sigma Chemical); (c) 1 U/ml chondroitinase ABC (Sigma Chemical), (d)0.05% trypsin (Life Technologies); and (e) 1100 U/ml hyaluronidasefollowed by 380 U/ml collagenase (7.5 min. in each). The days when celloutgrowth (round cells separated from the explant) and cell attachment(elongated cells) were first evident were recorded. All cultures wereterminated after 30 days. If no outgrowth was noted, time to outgrowthwas assigned 28 or 30 days for exps. 1 and 2, respectively. Explantsallocated for immunohistochemistry were fixed in 10% formalin, paraffinembedded and cut to 7 μm sections. Sections were stained with a α-smmonoclonal antibody (Sigma Chemical, St. Louis, Mo.). Statisticalanalysis was performed by ANOVA with Fisher's PLSD post-hoc test.

Results.

The time to cell attachment after outgrowth from untreated explantswas >4 weeks with no sign of outgrowth in 6 of 9 explants. There was asignificant effect of collagenase treatment time on the time to cellattachment (p<0.001).

TABLE 2 Times to cell attachment after collangenase treatments ofcartilage explants Explant Treatment Days Untreated 27.2 ± 0.4   1-mincollangenase 15.4 ± 2.6   5-min collangenase 9.9 ± 1.0 10-mincollangenase 6.2 ± 0.4 15-min collangenase 5.9 ± 0.4 (Mean ± SEM: n = 9)

Treatments with hyaluronidase, chondroitinase ABC, and trypsin, had noeffect on the times to outgrowth and attachment (TABLE 3). In contrast,the collagenase treatment yielded a time to outgrowth of at least 1order of magnitude less than the untreated group (2.2±0.2 vs 27.7±1.5days, respectively; TABLE 3). Treatment of the explants withhyaluronidase+collagenase yielded results that were comparable totreatment with collagenase alone. Signs of attachment of the outgrowthcells were generally found within 3 days of the first evidence ofoutgrowth.

TABLE 3 Times to outgrowth and attachment of chondrocytes from articularcartilage explants after various enzymatic treatments Time to OutgrowthTime to Attachment Group (days) (days) Untreated 27.7 ± 1.5 28.5 ± 1.0Collagenase  2.2 ± 0.2  5.8 ± 0.6 Hyaluronidase 25.0 ± 1.6 27.5 ± 0.9Chondroitinase ABC 29.2 ± 0.8 29.7 ± 0.3 Trypsin 28.8 ± 1.2 29.5 ± 0.5Hyaluronidase +  2.5 ± 0.3  5.0 ± 0.4 Collagenase (Mean ± SEM; n = 6)

Immunohistochemistry revealed that approximately 70% of the chondrocytesin the explants stained positive for the α-sm isoform (TABLE 4). Thechromogen was restricted to the cytoplasm of the cells that displayedthe typical chondrocyte morphology and location in lacunae. There was nosignificant difference in the percentage of α-sm-staining cells in theexplants in the collagenase and untreated control groups, at any timeperiod in culture (TABLE 4). There were significant increases in thepercentage of α-sm-containing cells in the untreated andcollagenase-treated groups after 14 days in culture, compared to theinitial values (TABLE 4; p<0.02 and p<0.01, respectively). After 20days, there was a decrease in the number of cells in all explants and asignificant reduction (p<0.0001) in the % of α-sm-containing cells inthe explants, compared to 14 days (TABLE 4). The percentage of attachedcells from all groups that stained positive for α-sm was greater than90%.

TABLE 4 The percentage of cells in untreated and collangenase- treatedarticular cartilage explants containing α-smooth muscle actin, aftervarious time in culture Groups Initial 6 days 14 days 20 days Untreated68 ± 9 78 ± 7 92 ± 5 49 ± 11 15-min collagenase 74 ± 8 93 ± 2 98 ± 2 51± 5  (Mean ± SEM; n = 6)

Discussion.

The notable findings of this EXAMPLE were that the rate of chondrocyteoutgrowth from adult human articular cartilage could be profoundlyaccelerated by collagenase treatment and that chondrocytes in adulthuman asteoarthritic articular cartilage contain a contractile actinisform not previously identified in this cell type. The investigation ofcartilage from joints with arthritis is useful, as this is thepopulation that may benefit from faciliated cartilage repair. Theresults of this EXAMPLE show that collagen architecture limitschondrocyte migration. Thus, we show that, if migration of chondrocytesto a wound edge in vitro can be facilitated, the cells contribute to thehealing process by contracting an endogenous or exogenous scaffoldbridging the defect.

Example 9 Histologic Changes in the Human Anterior Cruciate Ligamentafter Rupture

This EXAMPLE was designed to determine: (a) whether the rupturedanterior cruciate ligament remnant was capable of maintaining cellswithin its substance after rupture, in the intrasynovial environment;(b) whether an increase in cell number density would occur in theanterior cruciate ligament after complete rupture; and (c) whether theruptured ligament would revascularize after injury. Another objectivewas to determine if cells with a contractile actin isoform, α-sm actinwere present in the healing human anterior cruciate ligament.

Methods.

Twenty-three ruptured anterior cruciate ligament remnants were obtainedfrom seventeen men and six women (ages twenty to forty-six, averagethirty-one years), undergoing anterior cruciate ligament reconstruction(TABLE 5). The ruptured ligaments were obtained from ten days to twoyears after rupture. Ten contemporaneous intact ligaments were obtainedfrom three men and seven women (ages fifty seven to eighty-three,average sixty-nine years) undergoing total knee arthroplasty fordegenerative joint disease (TABLE 5). The intact ligaments were resectedfrom their insertion sites with a scalpel by the surgeon. The majorityof the ruptured ligaments were gently lifted from the posterior cruciateligament, transected at their tibial attachment, and removedarthroscopically by the surgeon. Ruptured ligaments retrieved at tendays to three weeks were removed at the time of open reconstruction formultiple ligament injury.

TABLE 5 Patient Demographics for Intact and Ruptured ACL tissue IntactLigaments Ruptured Ligaments Patient Age Patient Age Time from No.(years) Gender No. (years) Gender rupture* 1 61 Man 11 34 Man 1 week 265 Woman 12 25 Man 3 weeks 3 65 Woman 13 28 Woman 3 weeks 4 83 Woman 1445 Woman 4 weeks 5 73 Woman 15 24 Man 6 weeks 6 75 Woman 16 24 Woman 6weeks 7 62 Woman 17 14 Woman 8 weeks 8 65 Man 18 20 Woman 8 weeks 9 65Woman 19 24 Man 8 weeks 10 71 Man 20 29 Man 8 weeks 21 45 Man 12 weeks 22 42 Man 16 weeks  23 41 Man 16 weeks  24 24 Man 16 weeks  25 31 Man 16weeks  26 46 Man 20 weeks  27 34 Man 20 weeks  28 30 Man 52 weeks  29 22Man 64 weeks  30 21 Man 104 weeks  31 20 Man 104 weeks  32 44 Woman 104weeks  33 36 Man 156 weeks  *Time from rupture designated to the nearestweek, or the nearest 4 week period for the later specimens.

Histology and Immunohistochemistry.

The ligaments were marked with a suture at the site of tibialtransection, and fixed in neutral buffered formalin for one week. Afterfixation, specimens were embedded longitudinally in paraffin and 7 μmthick longitudinal sections were microtomed and fixed onto glass slides.Representative sections from each ligament were stained with hematoxylinand eosin and with a monoclonal antibody to α-sm actin (Sigma Chemical,St Louis, Mo., USA). In the immunohistochemical procedure,deparaffinized, hydrated slides were digested with 0.1% trypsin (SigmaChemical, St. Louis, Mo., USA) for 20 minutes. Endogenous peroxidase wasquenched with 3% hydrogen peroxide for 5 minutes. Nonspecific sites wereblocked using 20% goat serum for thirty minutes. The sections were thenincubated with the mouse monoclonal antibody to α-sm actin for 1 hr atroom temperature. A negative control section on each microscope slidewas incubated with non-immune mouse serum diluted to the same proteincontent, instead of the α-sm actin antibody, to monitor for non-specificstaining. The sections were then incubated with a biotinylated goatanti-mouse IgG secondary antibody for thirty minutes followed by thirtyminutes of incubation with affinity purified avidin. The labeling wasdeveloped using the AEC chromogen kit (Sigma Chemical, St Louis, Mo.)for 10 minutes. Counterstaining with Mayer's hematoxylin for twentyminutes was followed by a 20-minute tap water wash and coverslippingwith warmed glycerol gelatin.

Method of Evaluation.

Histological slides were examined using a Vanox-T AH-2 microscope(Olympus, Tokyo, Japan) with normal and polarized light. For thehistomorphometric measurements, the intact ligaments were evaluated atadjacent to the site of transection from the femoral attachment, and atone, two, four and six mm distal to the transection. These analyses didnot include the ligament insertion into bone. The ruptured ligamentswere evaluated at the ruptured edge, and at 1, 2, 4 and 6 mm distal tothe site of rupture (toward the tibial insertion). At each location,three 0.1 mm areas were evaluated by determining the total cell numberdensity and the predominant nuclear morphology, and by calculating thepercentage of cells positive for the α-sm actin isoform. Between 20 and230 cells were counted at each of the three areas. At each location, thetotal number of cells was counted and divided by the area of analysis toyield the cell number density, or cellularity. The cell morphology wasclassified based on nuclear shape: fusiform, ovoid, or spheroid.Fibroblasts with nuclei with aspect ratios (i.e., length divided bywidth) greater than ten were classified as fusiform, those with aspectratios between five and ten as ovoid, and those with nuclear aspectratios less than five as spheroid. The total number of blood vesselscrossing the section at each location was divided by the width of thesection at each location to obtain a blood vessel density for eachlocation.

Smooth muscle cells surrounding vessels were used as internal positivecontrols for determination of α-sm actin positive cells. Positive cellswere those that demonstrated chromogen intensity similar to that seen inthe smooth muscle cells on the same microscope slide and that hadsignificantly more intense stain than the perivascular cells on thenegative control section. Any cell with a questionable intensity ofstain (e.g., light pink tint) was not counted as positive. The α-smactin positive cell density was reported as the number of stained cellsdivided by the area of analysis and the percentage of α-sm actinpositive cells was determined by dividing the number of stained cells bythe total number of cells in a particular histologic zone.

Polarized light microscopy was used to aid in defining the borders offascicles and in visualizing the crimp within the fascicles. Measurementof the crimp length was performed using a calibrated reticule underpolarized light.

After the complete in-substance rupture of the human anterior cruciateligament, four progressive chronological phases of healing response wereseen.

Phase I. Inflammation.

Within the first few weeks post-rupture, the synovial fluid encounteredon entering the joint was rust-colored, and was easily suctioned fromthe knee. No blood clots were found within the knee joint. The entireremnants were swollen and edematous and the synovial and epiligamentoustissue was grossly disrupted. Blood clot was seen covering part of theligament remnants, but no connection between the femoral and tibial endswas visible grossly. Near the site of rupture, the ligament ends were offriable, stringy, tissue previously described as “mop-ends” (FIG. 12A).

Histologically, the ligament remnants retrieved in this time period werepopulated by fibroblasts and several types of inflammatory cells:polymorphonuclear neutrophils, lymphocytes, and macrophages. Theinflammatory cells were found in greatest concentration around bloodvessels near the site of injury. Macrophages appeared to be activelyphagocytosing cell and tissue debris.

Arterioles near the site of injury were noted to be dilated, withintimal hyperplasia (FIG. 12A) consisting of dramatic smooth muscle cellwall proliferation and thickening. Venules were noted to be dilated,with less evident smooth muscle cell hyperplasia. Capillaries appearedcongested, with rouleaux and thrombus formation noted in their lumens.

The collagenous extracellular matrix appeared disorganized and edematousnear the site of injury. Loss of the regular organization of thecollagen fibers was evident (FIG. 12A) and replacement withdisorganized, less dense, amorphous tissue was seen. The cellspopulating this amorphous tissue consisted of both fibroblasts andinflammatory cells. At the site of rupture, several adjacent ruptureddistal fascicles were bridged by a fibrin clot at ten days, and severalof the ruptured fascicle ends were covered by a twenty- to fiftymicrometer thick fibrin clot. However, no gaps larger than 700micrometers contained any bridging material.

Phase II. Epiligamentous Regeneration.

Between three and eight weeks after rupture, gradual growth ofepiligamentous tissue with a synovial sheath was noted over the rupturedend of the ligament remnant, giving it a smoother, mushroom appearance,different from the mop-ends seen in the earlier specimens (FIG. 12B). Notissue was noted to bridge the gap between the proximal and distalsegments, although several of the distal remnants were adherent to thesheath of the intact posterior cruciate ligament.

Histologically, the epiligamentous regeneration phase was characterizedby a relatively unchanging cell number density and blood vessel densityin the ligament remnant. After the initial influx of inflammatory cellsand removal of cell and tissue debris seen in the inflammatory stage,the number of inflammatory cells decreased, and fibroblasis became thedominant cell type. The cell number density of fibroblasts was similarto that seen in the uninjured ligament and the remaining blood vesselsdisplayed near normal morphologies, with little intimal hyperplasia. Noneovascularization was noted within the ligament fascicles.

Most of the changes occurred in the epiligament that displayed anincrease in cell number density and blood vessel density. The vascularepiligamentous tissue was noted to gradually extend over the rupturedligament end, encapsulating the mop-ends of the individual capsules.Thickening of the epiligament and fibroblast proliferation were seen tooccur during this time period. A synovial layer, similar to that seencovering the epiligamentous tissue in the intact anterior cruciateligament, was noted to form over the extending neoepiligamentous tissue.

Phase III. Proliferation.

By eight weeks, the distal anterior cruciate ligament remnants werecompletely encapsulated by a synovial sheath, and few remaining mop-endswere seen grossly (FIG. 12C). No tissue was visible between the proximaland distal ligament remnants. Several of the distal remnants were notedto be adherent to the periligamentous tissue of the posterior cruciateligament.

Histologically, the period between eight and twenty weeks after rupturewas characterized by increasing cell number density and blood vesseldensity in and among the fascicles of the ligament remnant. Fibroblastswere the predominant cell type, and the entire remnant becameincreasingly cellular, with a peak cell number density at sixteen totwenty weeks. The cellular orientation remained disorganized, with fewcell nuclei with longitudinal axes parallel to that of the ligament.Vascular endothelial capillary buds were seen during this phase, andloops from anastomoses of proximal sprouts were noted to form a diffusenetwork of immature capillaries (FIG. 12C).

The collagenous material of the ligament fascicles remained disorganizednear the site of injury. No preferential orientation was seen; however,bands of parallel collagen fibers were noted to begin to form anddevelop a waveform similar to the crimp seen in the intact humananterior cruciate ligament. These areas were a small component of theremnant, and the longitudinal axis of the waveform was rarely alignedwith the longitudinal axis of the ligament remnant.

The epiligamentous tissue remained vascular and was relatively unchangedin appearance throughout this phase. The synovial layer persisted as atwo-cell layer continuous over the epiligamentous tissue.Immunohistochemistry revealed α-sm actin containing cells distributedthroughout the intact and ruptured ligaments, albeit in relatively lowpercentages (TABLE 6). Of note was the abundance of such cells incertain regions of the synovium and epiligamentous tissue. In somecases, the α-sm actin cells in the synovium were clearly separate fromvascular smooth muscle cells and pericytes in the underlyingepiligamentous tissue. In many areas, however, such a distinction wasnot possible as the synovium merged with a highly vascular epiligament.

TABLE 6 Histomorphometric measurements of the intact and ruptured humananterior cruciate ligament Proximal 1 mm 2 mm 4 mm 6 mm Weeks out fromrupture edge from edge from edge from edge from edge Intact LigamentsCell density(#/mm²)* 701 ± 120 525 ± 108 539 ± 91  294 ± 39  265 ± 37 Nuclear aspect ratio 6.1 ± 0.9 4.5 ± 0.8 4.3 ± 0.6 3.6 ± 0.6 2.4 ± 0.5Blood vessel density (#/mm)  1.5 ± 0.16 1.2 ± 0.2 1.0 ± 0.2 0.60 ± 0.120.24 ± 0.03 % of cells positive for SMA 4.7 ± 1.0 7.3 ± 1.7 10.7 ± 3.0  15 ± 3.9  17 ± 4.3 n 10  10  10  10  10  1 to 6 weeks Celldensity(#/mm2)* 614 ± 249 476 ± 267 420 ± 210 254 ± 48  231 ± 30 Nuclear aspect ratio 4.5 ± 1.0 3.9 ± 0.8 3.7 ± 0.9 4.2 ± 0.7 4.3 ± 1.2Blood vessel density (#/mm)  4 ± 3.3 2.9 ± 2.6 5.0 ± 2.9 2.0 ± 1.2 0.8 ±0.2 % of cells positive for SMA 2.3 ± 1.4 1.9 ± 1.1 1.0 ± 0.3 0.83 ±0.31 0.36 ± 0.12 n 6 6 6 6 6 8 to 12 weeks Cell density(#/mm2)* 1541 ±451  1272 ± 363  965 ± 249 701 ± 162 497 ± 151 Nuclear aspect ratio 6.2± 1.0 4.3 ± 1.0 3.8 ± 1.0 2.9 ± 1.0 4.1 ± 1.3 Blood vessel density(#/mm) 5.1 ± 3.1 4.0 ± 2.6 3.0 ± 2.1 2.2 ± 1.0 2.1 ± 1.0 % of cellspositive for SMA  1.3 ± 0.76  1.3 ± 0.28  1.1 ± 0.33 0.5 ± 0.3 0.33 ±0.19 n 5 5 5 5 5 16 to 20 weeks Cell density(#/mm2)* 2244 ± 526  1522 ±285  1037 ± 280  833 ± 312 1009 ± 437  Nuclear aspect ratio 5.4 ± 1.04.8 ± 0.2 4.6 ± 0.5 5.3 ± 1.2 3.8 ± 1.3 Blood vessel density (#/mm) 13.3± 4.9  4.0 ± 1.3 5.2 ± 2.0 2.9 ± 1.6 3.3 ± 2.0 % of cells positive forSMA 0.58 ± 0.26 0.42 ± 0.2  0.31 ± 0.16 0.25 ± 0.25  1.2 ± 0.65 n 6 6 66 6 52 to 104 weeks Cell density(#/mm2)* 559 ± 115 601 ± 204 718 ± 241590 ± 46  546 ± 45  Nuclear aspect ratio 3.7 ± 0.6 4.0 ± 0.9 4.2 ± 0.53.3 ± 1.1 3.7 ± 0.5 Blood vessel density (#/mm) 2.1 ± 2.0 1.5 ± 1.3 1.2± 0.7 1.6 ± 0.8 1.3 ± 0.6 % of cells positive for SMA 0.5 ± 0.3 0.22 ±0.16 0.19 ± 0.11 0.53 ± 0.26 1.1 ± 0.9 n 6 6 6 6 6 *all values are ±SEM.

Phase IV. Remodeling and Maturation.

Between 1 and 2 years after ligament rupture, remodeling and maturationof the ligament remnant were seen. The ligament ends were dense andwhite, with little fatty synovium seen overlying them (FIG. 12D). Notissue was noted to connect the two ends of the ligament.

Histologically, the fibroblast nuclei were increasingly fusiform withthe long axis of the nucleus aligned with the longitudinal axis of theligament. There was decreased blood vessel density within the ligamentremnant. The epiligamentous tissue continued to decreased in thickness;however, the synovial sheath persisted. A more axial alignment of thecollagen fascicles was seen. The cell number density decreased to alevel similar to that seen in the intact human anterior cruciateligament.

Histomorphometry.

The numeric results for the ligaments at each of the time points areprovided in TABLE 6. The evaluation of the percentage of α-smactin-positive cells did not include the synovium or the epiligamentoustissue where the distinction of vascular and non-vascular cells couldnot be confidently made.

In the intact control group of anterior cruciate ligaments, there was adecrease in cell number density and vascularity proceeding from proximalto distal and an increase in the sphericity of the cell nuclei, and inthe percentage of α-sm actin-positive cells.

Two-way ANOVA demonstrated that the cell number density in the humanruptured anterior cruciate ligament was significantly affected bylocation in the ligament remnant and time after rupture. The cell numberdensity was highest near the site of injury at all time points. Thiscellularity increased significantly to a maximum at sixteen to twentyweeks (FIG. 13; Bonferroni-Dunn post-hoc testing, p<0.005) and decreasedbetween twenty and fifty-two weeks after injury (Bonferroni-Dunnpost-hoc testing, p<0.005). With the number of ligaments available, ageand gender were not found to significantly affect cell number density(two-way ANOVA, p>0.80 and p<0.40, respectively).

The morphology of the cell nuclei was also significantly affected by thelocation in the ligament remnant, but not by time after injury, genderor age. Using two-way ANOVA, the proximal part of the ligament remnantwas found to have cells with a higher nuclear aspect ratio when comparedwith cells in the more distal remnants (Bonferroni-Dunn post-hoctesting, p<0.0005). This pattern was also observed in the intactligaments. Two-way ANOVA demonstrated that the morphology of the cellnuclei was significantly affected by the location in the ligamentremnant (p<0.003), but with the numbers available, not by time afterinjury (p<0.40) or age (p<0.70). The effect of gender on this parameterwas close (p<0.06) to meeting our criterion for significance (p<0.05)with the number of ligaments analyzed.

The blood vessel density was found to be significantly affected by thetime after injury with two-way ANOVA. The blood vessel density reachedits highest value at sixteen to twenty weeks (Bonferroni-Dunn post-hoctesting, p<0.003) and decreased after that time point (TABLE 6). Theblood vessel density decreased with distance from the ruptured edge(FIG. 14). While the effect of location on blood vessel density (p<0.09)did not reach the acceptance criterion of p<0.05 for significance usingANOVA with the number of ligaments available, its p value andexamination of the data suggest a higher density of vessels near thesite of injury. With the numbers available, two-way ANOVA found nosignificant effect on blood vessel density for age (p<O) or gender(p>0.25).

Cells which stained positive for the α-sm actin isoform were presentthroughout the intact and ruptured anterior cruciate ligament. Cellswith all three morphologies were noted to stain positive. While two-wayANOVA found no significant effect of time after injury on α-sm actinstaining (p<0.30) with the number of ligaments available, the rupturedligaments had a smaller percentage of cells which stained positive whencompared with the intact ligaments (TABLE 6). Two-way ANOVA also foundno significant effect of location in the ligament (p<0.90), or age ofthe patient (p<0.61) on the percentage of cells staining positive forα-sm actin with the numbers available. Gender was found to have asignificant effect on α-sm actin expression, with women having a greaterpercentage of cells staining positive for the α-sm actin isoform thanmen (p<0.002).

Discussion.

The response to injury is similar to that reported in other denseconnective tissues with two exceptions: the presence of a epiligamentousregeneration phase which lasts eight to twelve weeks, and the lack ofany tissue bridging the rupture site. Other characteristics reported indense connective tissue healing, such as fibroblast proliferation,expression of α-sm actin and angiogenesis are all seen to occur in thehuman anterior cruciate ligament.

The finding of a epiligamentous regeneration phase distinguishes theruptured human anterior cruciate ligament from other connective tissueswhich heal successful and reconciles the other findings in this EXAMPLEof a productive response to injury with previous reports of failure ofthe anterior cruciate ligament cells to respond to rupture. The presenceof the epiligamentous regeneration phase in this EXAMPLE illustrates theimportantance of analyzing the results of primary repair or augmentationtechniques. These procedures may have different results depending on thetiming of repair after injury. Repair done in the first few weeks afterinjury may result in filling of the gap with the proliferativeepiligamentous vascular tissue which is active at that time. Repairperformed months after injury, when the endoligamentous tissue isproliferating, may result in a different mode of repair.

This EXAMPLE also demonstrates the lack of any tissue seen in the gapbetween the ligament remnants. In extra-articular tissues whichsuccessfully heal, the fibrin clot forms and is invaded by fibroblastsand gradually replaced by collagen fibers. This has been demonstrated tobe instrumental in the healing process in both tendon (Buck, 66 J.Pathol. Bacteriol. 1-18 (1953) and the medial collateral ligament (Franket al., 1 J. Orthop. Res. 179-188 (1983)). In the human anteriorcruciate ligaments studied here, only one of the ruptured ligamentsdemonstrated any fibrin clot bridging adjacent fascicles of the tibialremnant, and none of the ruptured ligaments had any clot or tissuebridging the proximal and distal remnants, or bridging gaps greater than700 micrometers. As the early specimens were obtained using an opentechnique, it is possible that the blood clot seen on the remnantsformed at the time of surgery, after the synovial fluid had been removedfrom the joint. In the knees operated on in the first ten to twenty onedays after injury, the hemarthrosis had already been lysed to a viscousliquid incapable of holding the ruptured ligament remnants together.

This EXAMPLE provides guidance for the analysis of human tissue that hasbeen ruptured and maintained in an in vivo, intrasynovial environmentuntil the time of retrieval.

Example 10 The Migration of Cells from the Ruptured Human AnteriorCruciate Ligament into Collagen-Based Regeneration Templates

Introduction.

The overall object of the invention is to restore only the ligamenttissue which is damaged during rupture, while retaining the rest of theligament. The model used in this EXAMPLE involves filling the gapbetween the ruptured ligament ends with a bioengineered regenerationbridge, or template, designed to facilitate cell ingrowth and guidedtissue regeneration. In this EXAMPLE, we investigated one of thecritical steps in guided tissue regeneration; namely, the ability ofcells in the adjacent injured ligament tissue to migrate into theregeneration template. This EXAMPLE focuses on whether the cells of thehuman anterior cruciate ligament cells are able to migrate to a templateafter the anterior cruciate ligament has been ruptured. We also wantedto determine whether the cells which migrated expressed a contractileactin isoform, α-sm actin, which may contribute to contraction of thetemplate and self-tensioning of the ligament.

Methods.

Four ruptured anterior cruciate ligaments were obtained from 4 menundergoing anterior cruciate ligament reconstruction, ages 25 to 34,with an average age of 28 years. Time between injury and ligamentretrieval ranged from 6 to 20 weeks. Synovial tissue covering theligaments was removed and the ligament remnants cut lengthwise into twosections. One longitudinal section from each ligament (n=4) wasallocated for histology. The remaining section was transected intothirds along its length. Each section was divided into 5 biopsies, orexplants, four of which were placed into culture with thecollagen-glycosaminoglycan regeneration template, and one of which wasplaced onto a petri dish for 2-D explant culture (FIG. 15). The siteclosest to the rupture, or injury zone, contains a higher cell numberdensity than that of the more distal remnant, which resembles thehistology of the intact anterior cruciate ligament. Therefore, the moredistal remnant (normal zone) was used as an age and gender matchedcontrol for the tissue obtained at the site of injury (injury zone) and0.5 cm distal to the site of injury (middle zone).

Explant Culture on a 2-D Surface.

The 12 tissue biopsies from the three sections of the four ligamentswere explanted onto tissue-culture treated 35 mm wells (Corning #430343,6 well plates, Cambridge, Mass.) and cultured in 1 cc of mediacontaining Dulbecco's DMEMI F12 with 10% fetal bovine serum, 2%penicillin streptomycin, 1% amphotericin B, 1% L-glutamine and 2%ascorbic acid. Media was changed 3× a week. Outgrowth from the explantbiopsies was recorded every three days as the surface area covered byconfluent fibroblasts. The area of outgrowth was measured using aninverted microscope and a transparent grid sheet. The number of squarescovered by the confluent cells was counted and the area calculated bymultiplying the number by the known area of each square. The effectiveradius of outgrowth was calculated by dividing the total area ofconfluent cells by π (3.14) and taking the square root of the result.The rate of outgrowth was then calculated by plotting the averageeffective radius of outgrowth as a function of time since confluentoutgrowth was first observed and calculating the slope of the linearrelationship. Seven zones were not found to be statistically significant(p=0.66). Two way ANOVA demonstrated the effect of explant location inthe ligament had a significant effect on cell number density, but thattime in culture did not have a significant effect. Cells migrating intothe collagen-glycosaminoglycan scaffold demonstrated all of the threepreviously described ligament fibroblast morphologies: fusiform orspindle-shaped, ovoid, and spheroid.

The maximum cell number density in the template at the four week timeperiod was found to directly correlate with cell number density of theexplant tissue (r²=0.24), to inversely correlate with density of bloodvessels in the explant tissue (r²=0.28), and not to correlate with thepercentage of α-sm actin positive cells in the explant tissue (r²=0.00).All cells which migrated into the C template were found to be positivefor α-sm actin at the 1 and 2 week period.

Template Contraction.

The templates were noted to decrease in size during the four weeks ofculture. Those templates cultured without tissue contracted an averageof 19.0%+0.7%. Templates cultured with tissue contracted between 17 and96%. A greater maximum cell number density of α-sm actin positive cellswithin the template was found to correlate with a greater rate ofscaffold contraction (r²=0.74).

The 3-D culture substrate used in this EXAMPLE was a highly porouscollagen-glycosaminoglycan matrix, composed of type I bovine hidecollagen and chondroitin-6-sulfate, prepared by freeze-drying thecollagen-glycosaminoglycan dispersion under specific freezing conditions(Yannas et al., 8 Trans Soc Biomater. 146 (1985)) to form a tube withpore orientation preferentially oriented, longitudinally. The averagepore size of the collagen-glycosaminoglycan scaffold manufactured inthis manner has previously been reported as 100 gm (Chamberlain, LongTerm Functional And Morphological Evaluation Of Peripheral NervesRegenerated Through Degradable Collagen Implants. (M.S. ThesisMassachusetts Institute of Technology, 1998)(on file with the MITLibrary)).

Immunohistochemistry.

The expression of α-sm actin was determined using monoclonal antibodies.For the 3-D culture specimens, deparaffinized, hydrated slides weredigested with 0.1% trypsin (Sigma Chemical, St. Louis, Mo., USA) for 20minutes. Endogenous peroxide was quenched with 3% hydrogen peroxide for5 minutes. Nonspecific sites were blocked using 20% goat serum for 30minutes. The sections were then incubated with mouse anti-α-sm actinmonoclonal antibody (Sigma Chemical, St. Louis, Mo., USA) for one hourat room temperature. Negative controls were incubated with mouse serumdiluted to an identical protein content. The sections were thenincubated with biotinylated goat anti-mouse IgG secondary antibody for30 minutes followed by thirty minutes of incubation with affinitypurified avidin. The labeling was developed using the AEC chromagen kit(Sigma Chemical, St. Louis, Mo.) for ten minutes. Counterstaining withMayer's hematoxylin for 20 minutes was followed by a 20 minute tap waterwash and coverslipping with warmed glycerol gelatin.

Histology of the Ligament Fascicles.

The proximal one-third was populated predominantly by fusiform and ovoidcells in relatively high density, and the distal two-thirds waspopulated by a lower density of spheroid cells. The levels oftransection used to obtain the biopsies were resulted in an injury zonewhich contained an average cell number density of 2083+982 cells/mm²(n=4), a middle zone with an average cell number density of 973+397cells/mm² (n=4), and a normal zone with an average cell density of803+507 cells/mm² (n=4). The cell number density in the injury zone washigher in the specimen obtained twenty weeks after injury (4318cells/mm², n=1) when compared with the remnants obtained six weeks (394cells/mm², n=1) and eight weeks after injury (1811 cells/mm², n=2). α-smactin immunohistochemistry of the ruptured ligaments showed positivestaining in 2 to 20% of fibroblasts not associated with blood vessels.

2-D Culture Outgrowth.

The outgrowth of cells onto the 2-D culture dishes was observed to occuras early as 3 days and as late as 21 days, with outgrowth first detectedat an average of 6.6±2.0 days after explanting. Explant size was notfound to correlate with the time of onset or rate of outgrowth. Linearregression analysis of the plot of effective outgrowth radius versustime for all explants that demonstrated confluent outgrowth had acoefficient of determination of 0.98. The average rate of outgrowth,represented by the slope of this plot, was 0.25 mm/day.

3-D Culture Outgrowth.

In the constructs with interposed collagen-glycosaminoglycanscaffolding, fibroblasts migrated from the human anterior cruciateligament explants into the templates at the earliest time point (1week). At one week, migration into the templates was seen in 4 of 4 ofthe templates cultured with explants from the injury zone, 1 of 4templates cultured with explants from the middle zone, and 1 of 4 of thetemplates cultured with explants from the normal zone. By four weeks,cells were seen in 3 of 3 templates cultured with the injury zoneexplants (the fourth template had been completely degraded) and in 3 offour of the templates cultured with the normal zone explants. Five ofthe explants completely degraded the template prior to the collectiontime. The location from which the explants were taken (injury, middle ornormal) was found to have a statistically significant effect on the cellnumber density in the template (two way ANOVA, p=0.001), withBonferroni-Dunn post-hoc testing demonstrating differences betweentemplates cultured with explants from the injury zone and middle zone(p=0.009) and the injury and normal zone (p=0.003; FIG. 16). Thedifference between the template cell density for templates cultured withexplants from the middle and tibial of the twelve explants (three fromthe injury zone, two from the middle zone, and two from the normal zone)demonstrated confluent growth for at least two consecutive time periodsprior to termination and were included in the calculation of the averagerate. All explanted tissue and fibroblasts on the culture wells werefixed in formalin after four weeks in culture.

Fascicular-Collagen-Glycosaminoglycan Template Constructs.

One fascicle from each of the 4 patients was divided into explants foruse in the test (injury zone or middle zone and template) and control(normal zone and template) groups. This yielded two test and one controlconstruct per patient for examination after 1, 2, 3, and 4 weeks inculture, providing eight test and four control constructs at each of thefour time points.

The forty-eight constructs were made by placing the ligament explantonto a 9 mm disc of collagen-glycosaminoglycan (CG) template (FIG. 15).All of the constructs were cultured in media containing Dulbecco's DMEMIF12 with 10% fetal bovine serum, 2% penicillin streptomycin, 1%amphotericin B, 1% L-glutamine and 2% ascorbic acid. Media was changed3× a week. The diameter of the template was measured at each mediachange. Six templates without explants were cultured simultaneously andmeasured at each time change as controls.

One construct from the injury, middle and normal zones from each patient(n=4) were fixed and histologically examined after 1, 2, 3 and 4 weeksin culture. Two of the constructs at three weeks showed signs oflow-grade infection and were excluded from the EXAMPLE. Hematoxylin andeosin staining and immunohistochemical staining for α-sm actin wereperformed for each construct. Sections were examined using a Vanox-TAH-2 microscope (Olympus, Tokyo, Japan) with normal and polarized light.For each template, areas of 0.1 mm² (250 by 400 micrometers) werecounted, and the highest cell number within that area recorded as themaximum cell number density. This value was multiplied by 10 to obtainthe number of cells per square millimeter. The fascicular tissue andcollagen-glycosaminoglycan scaffolding were examined using polarizedlight to determine the degree of crimp and collagen alignment.

This EXAMPLE demonstrated that the cells intrinsic to the ruptured humananterior cruciate ligament were able to migrate into a regenerationtemplate, eventually attaining small areas with cell number densitiessimilar to that seen in the human anterior cruciate ligament in vivo.Explants from the transected region demonstrated outgrowth onto a 2-Dsurface with a linear increase in outgrowth radius as a function of timein culture. Cells which migrated into the collagen-glycosaminoglycanscaffold differed significantly from the populations of the rupturedanterior cruciate ligament in that while an average of 2 to 20% of cellsare positive for α-sm actin in the ruptured anterior cruciate ligament,100% of cells noted to migrate at the early time periods were positivefor this actin isoform.

The investigation in this EXAMPLE implemented an in vitro model thatallows for the investigation of the migration of cells directly from anexplant into a 3-D collagen-glycosaminoglycan scaffold. Cells with allthree previously described ligament fibroblast morphologies—fusiform,ovoid and spheroid—were noted to migrate into the scaffold. Location inthe ligament from which the explant was obtained was found tosignificantly effect the cell number density in the template, withhigher number densities of cells found to migrate from the injury zoneof the ligament. These findings suggest that cells intrinsic to thehuman anterior cruciate ligament are capable of migrating from theirnative extracellular matrix onto an adjacent collagen-glycosaminoglycanscaffold, and that the zone of injury contains cells in which arecapable of populating a regeneration template in greater numbers thanthe middle and normal zones of the ruptured ligament.

The outgrowth rates noted for the explants from ruptured ligaments wasfound to be about 0.25 mm/day. However, the average time to outgrowthwas four days shorter for the ruptured anterior cruciate ligamentexplants (6.6±2.0 days) than that reported for the intact anteriorcruciate ligament explants (10±3 days) (Murray et al., 17(1) J. Orthop.Res. 18-27 (1999)).

The cellular response to injury appears to be the appropriate one in theanterior cruciate ligament; however, no regeneration of the tissue inthe gap between ruptured ends is noted. Previous investigators havedemonstrated that coagulation of blood does not occur in theintrasynovial environment. As the initial phase of healing inextra-articular tissues involves formation of a blood clot whichre-connects the ruptured ends of the ligament, one hypothesis for thelack of healing of the anterior cruciate ligament after injury may bethe lack of formation of a provisional scaffolding due to thecoagulation defect in the knee. Therefore, use of a bioengineeredsubstitute for the provisional blood clot may facilitate the healing ofthe intra-articular anterior cruciate ligament.

Conclusions.

Cells from the human anterior cruciate ligament are capable of migratinginto an adjacent regeneration template in vitro. Cells migrate in thegreatest density from the zone nearest the site of rupture, or injuryzone when compared with tissue taken far from the site of injury. Thissuggests the approach of developing a ligament regeneration template, or“bridge”, which reconnects the ruptured ligament ends, may be successfulin facilitating ligament regeneration after rupture. The potentialadvantages of this approach over anterior cruciate ligamentreconstruction include preservation of the proprioceptive innervation ofthe anterior cruciate ligament, retention of the complex shape andfootprints of the anterior cruciate ligament, and restoration of thepre-injury knee mechanics. Successful regeneration of the anteriorcruciate ligament may lead to similar advances for meniscal andcartilage regeneration after injury.

This EXAMPLE shows the potential of cells from the ruptured humananterior cruciate ligament fibroblasts to migrate intocollagen-glycosaminoglycan templates that may ultimately be used tofacilitate regeneration anterior cruciate ligament after rupture. Themodel used here allows for the analysis of the migration of fibroblastsout of human tissues directly onto a porous 3-D scaffold in acontrolled, in vitro, environment. This construct obviates severalpossible confounding factors, such as modulation of cell phenotype,which may occur during cell extraction or 2-D cell culture.

Example 11 Effects of Location in the Human ACL on Cellular Outgrowthand Response to TGF-β1 In Vitro

The purpose of this EXAMPLE was to determine how cells in selectedlocations in the human anterior cruciate ligament varied in certainbehavior that might affect their potential for repair. Specifically, inthis EXAMPLE the outgrowth of cells in vitro from explants differentlocations in the anterior cruciate ligament, at two concentrations offetal bovine serum (FBS) and three concentrations of TGF-β1 weremeasured.

Methods.

Fifteen intact human anterior cruciate ligaments were retrieved frompatients undergoing TKA. The ligaments were cut transversely into four2-3 mm thick sections. Each section was divided into six explants, twoof which were reserved for histological analysis and four of which wereplaced in 2-D culture wells. Explants from the proximal and distalsections were cultured in 10% FBS, 0.5% FBS, and 0.5% FBS with 006ng/ml. TGF-β1, 0.6 ng/ml TGF-β1, and 6 ng/ml TGF-β1. Media were changed3× a week, and cell outgrowth area measured at each medium change.Cultures were terminated after four weeks.

Results.

Explants taken from the proximal anterior cruciate ligament differedsignificantly in their outgrowth behavior from those taken from thedistal anterior cruciate ligament. In the 10% FBS group, there was asignificant effect of location on the time to initial contiguousoutgrowth (ANOVA, p=0.03). There was, however, no effect of location onthe rate of outgrowth (ANOVA, p=0.14). In contrast, in the 0.5% FBSgroup the rates of outgrowth were different with a higher outgrowth rateseen in the proximal explants (ANOVA, p=0.01; FIG. 17). This was mostpronounced in the groups treated with 0.6 ng/ml of TGF-β1 (FIG. 18).Results of histological analysis of longitudinal sections of theligaments were consistent with previous observations of higher celldensities and nuclear aspect ratios in the proximal anterior cruciateligament. No correlation was found between the explant outgrowth rateand the cell number density (r²=0.04) or the predominant nuclearmorphology (r²=0.11).

Discussion.

This EXAMPLE demonstrates that explants taken from proximal and distalsites in human anterior cruciate ligament respond differently tolow-serum conditions, as well as to the addition of TGF-β1. Becausethese differences do not correlate with the cell number density ornuclear morphology, other features of the cellular heterogeneity andfibroblast phenotype within the human anterior cruciate ligament may beassociated with the differences in cell behavior.

Example 12 The Effect of Gender and Exogenous Estrogen on the Histologyof the Human Anterior Cruciate Ligament

The purpose of this EXAMPLE is to determine if any histologicaldifferences are present between the anterior cruciate ligament in womenand men. Another objective of this EXAMPLE was to determine if exogenousestrogen had any significant effect on the measured parameters byexamining ligaments from two groups of women, those on and off estrogenreplacement therapy.

Methods.

Intact anterior cruciate ligaments were obtained from 22 patientsundergoing total knee arthroplasty. Patients with rheumatoid arthritisor on non-steroidal anti-inflammatory medication were excluded from theEXAMPLE. Nine ligaments were obtained from men (ages 61 to 81, mean age71), seven from postmenopausal women (ages 51 to 83, mean age 69), andsix from postmenopausal women on estrogen replacement therapy (ERT; ages56 to 87, mean age 68). All ligaments were fixed in formalin, embeddedin paraffin, and 7 micrometer sections cut. Routine staining, as well asimmunohistochemistry for the α-sm actin isoform, was performed.Histomorphometry was performed on all ligaments, with analysis performedat the proximal edge of the ligament, and 1 mm, 2 mm, 4 mm and 6 mm fromthe proximal edge. At each location, three 0.1 mm² areas were analyzedfor total cell number, nuclear morphology, and percentage of cellsstaining positive for α-sm actin. The number of blood vessels at eachsite was counted and divided by the width of the section at that pointto yield a “blood vessel density.” Two-way ANOVA and unpaired Student ttesting were used to determine the statistical significance ofdifferences among groups.

Results.

Two-way ANOVA revealed a significant effect of location on cell numberdensity (p=0.002). While the cell density of the anterior cruciateligament was higher in women than in men at all sites, ANOVA yielded a pvalue greater than 0.05 (p>0.07). Unpaired Student t testing of celldensities at the proximal edge of the ligament, adjacent to the femoralinsertion, and at 1 mm from the proximal edge gave a value of p=0.05 forgender differences. Further distally in the ligament, the differencesbetween men and women were not statistically significant (p>0.10). Therewas no statistically significant difference in cell density betweenthose women on ERT and those not on estrogen replacement therapy(p=0.36). Age was not found to have a significant effect on the cellnumber density. Although women had a higher blood vessel density in theproximal region, this difference was not found to be statisticallysignificant. No statistically significant differences were found in thenuclear morphology or the percentage of α-sm actin positive stainingcells in the ligaments.

Discussion.

This EXAMPLE demonstrates that the histology of the human anteriorcruciate ligament is similar in men and women, with the exception of thecell number density in the proximal region, which is higher in womenthan men. This EXAMPLE also demonstrates that exogenous estrogen doesnot have an effect on cell number density, blood vessel density, cellnuclear morphology, or presence of α-sm actin.

Example 13 The Cellular Response to Injury in the Human AnteriorCruciate Ligament

This EXAMPLE was performed to determine if two of the biologic responsesrequired for regeneration of tissue, namely revascularization andfibroblast proliferation, occur in the human anterior cruciate ligamentafter injury.

Materials and Methods.

23 ruptured anterior cruciate ligament remnants were obtained frompatients (ages 20 to 46, avg. 31 years) at anterior cruciate ligamentreconstruction between 10 days and 2 years after rupture. Ten intactligaments were obtained from patients (ages 57 to 83, avg. 69 years) atTKA. Longitudinal sections were stained with a monoclonal antibody foralpha-smooth muscle actin (α-sm). Histomorphometric analysis was used todetermine the distribution of cell number density, blood vessel density,nuclear aspect ratio and the percentage of α-sm positive cells. Two-wayANOVA and Bonferroni-Dunn post-hoc testing determined statisticalsignificance.

Results.

No bridging clot or tissue was noted grossly between the femoral andtibial remnants for any of the ruptured ligaments. Four progressivephases of response were seen:

Phase I. Inflammation.

Inflammatory cells, dilated arterioles and intimal hyperplasia was seenbetween 1 and 3 weeks after rupture. Loss of the regular crimp patternwas noted near the site of injury, but maintained 4-6 mm from the siteof injury.

Phase II. Epiligamentous Regeneration.

Growth of epiligamentous tissue over the ruptured end of the ligamentremnant was noted between 3 and 8 weeks. Histologically, this phase wascharacterized by an unchanging blood vessel density and cell numberdensity within the remnant.

Phase III. Proliferation.

Between 8 and 20 weeks after rupture, a marked increase in cell numberdensity and blood vessel density within the ligament remnant was noted.Vascular endothelial capillary buds were noted to appear at thebeginning of this phase, and loops from anastomoses of proximal sproutsbegan to form a diffuse network of immature capillaries.

Phase IV. Remodeling and Maturation.

After one year from ligament rupture, the ligament ends were dense andwhite. Histologically, the fibroblast nuclei were increasingly uniformin shape and orientation. Decreased cell number density and blood vesseldensity were seen during this phase, to a level similar to that seen inthe intact human anterior cruciate ligament s.

Cell number density in the ligament after rupture was dependent on timeafter injury and distance from the injury site. The cell number densitywithin the ligament remnant peaked at 16 to 20 weeks (p<0.005), and washighest near the site of injury at all time points. Blood vessel densitywas dependent on time after injury, with a peak at 16 to 20 weeks(p<0.003). Cells staining positive for the contractile actin isoform,α-sm, were present throughout the intact and ruptured anterior cruciateligaments, but were not significantly effected by time after injury.

Example 14 Effects of Growth Factors and Collagen-Based Substrates theFibroinductive Properties of Fibroblast Migration

The purpose of this EXAMPLE is to determine the process offibroblast-mediated connective tissue healing and how specificalterations in the extracellular environment alter this process. Wequantify the effects of 4 different growth factors and 4 collagen basedsubstrates on features associated with the repair processes inconnective tissues which successfully heal. These processes are thefibroinductive properties of fibroblast migration, proliferation, andtype I, type II, and type III collagen synthesis. We also define theeffects of environmental modifications on the expression of acontractile actin isoform, α-smooth muscle actin (α-sm).

In EXAMPLE 3, we demonstrated that fibroblasts in the ruptured anteriorcruciate ligament are able to migrate from their native extracellularmatrix into a 3-D CG scaffold in vitro. This EXAMPLE provides improvedrates of migration, proliferation, and type I collagen synthesis ofanterior cruciate ligament fibroblasts by altering the degree and typeof cross-linking of the scaffold and by adding four different growthfactors to the scaffold. The specific aims for this EXAMPLE are (1) todetermine the effect of cross-linking of a collagen-based scaffold on(a) the rate of fibroblast migration, (b) the rate of fibroblastproliferation, (c) expression of a contractile actin, and (d) the rateof type I collagen synthesis by fibroblasts in the collagen-basedscaffold, and (2) to determine the effect of addition of selected growthfactors on these same outcome variables. Thus, this EXAMPLE determineshow specific alterations in scaffold cross-linking and the addition ofspecific growth factors alter the fibroinductive properties of acollagen based scaffold. In this EXAMPLE, the fibroinductive potentialof the scaffold is defined as its ability to promote fibroblastinfiltration, proliferation and type I collagen synthesis.

The following two hypotheses relate to the specific aims listed above:

The method and degree of cross-linking alter the rate of fibroblastmigration from an anterior cruciate ligament explant into acollagen-based scaffold as well as the rate of fibroblast proliferation,expression of a contractile actin, and type I collagen synthesis withinthe scaffold. The rationale for this hypothesis is the EXAMPLES above,which demonstrated that alteration in fibroblast proliferation rates andexpression of the contractile actin isoform after fibroblast seeding ofcross-linked scaffolds, as well as the differences in rates of collagensynthesis by chondrocytes seeded into type I and type II collagen basedscaffolds. One possible mechanism for this observation is that thesolubilized fragments of collagen resulting from the degradation of thecollagen-based scaffold could affect cell metabolism. These fragmentsmay form at different rates for different cross-linking methods.Validation of this mechanism demonstrates that the fibroinductiveproperties of the collagen-based scaffold can be regulated by the choiceof cross-linking method.

In this EXAMPLE, constructs of human anterior cruciate ligament explantsand cross-linked collagen-based scaffolds are used to determine therates of cell migration, proliferation, expression of a contractileactin and type I collagen synthesis. Scaffolds cross-linked withglutaraldehyde, ethanol, ultraviolet light and dehydrothermal treatmentare used. We correlate cross-linking method with the regulation of thefibroinductive properties of the scaffold.

(2) The addition of growth factors to the CG scaffold alters the ratesof fibroblast migration from an anterior cruciate ligament explant to acollagen-based scaffold as well as the rates of fibroblastproliferation, expression of a contractile actin, and type I collagensynthesis within the scaffold. The rationale for this hypothesis is thealteration in fibroblast migration rates onto 2-D surfaces and synthesisof type I collagen in vitro when growth factors are added to the culturemedia, as well as alteration in rates of incisional wound healing withthe addition of growth factors. Validation of this hypothesis shows howthe fibroinductive properties of the collagen-based scaffold may beregulated by the addition of a specific growth factor.

The growth factors to be studied in this EXAMPLE include TGF-β, EGF,bFGF and PDGF-AB. Constructs of human anterior cruciate ligamentexplants and collagen-based scaffolds cultured in media containinggrowth factors are used to determine the rates of cell migration,proliferation, expression of a contractile actin and type I collagensynthesis in these constructs. The control wells contain only 0.5% fetalbovine serum, a protocol which has been reported previously byDesRosiers et al., 14 J. Orthop. Res. 200-208 (1996). We correlategrowth factor presence with the regulation of the fibroinductiveproperties of the scaffold.

Assay Design.

The assay design is similar to that of EXAMPLE 4. Human anteriorcruciate ligament explants are obtained from patients undergoing totalknee arthroplasty. Ligaments which are grossly disrupted or demonstrategross signs of fatty degeneration are excluded from the analysis. Afairly uniform distribution of cells occurs in the distal ⅔ of theligament fascicles, so this section is used for all assays. Thepreparation of the collagen-based scaffold is as described in EXAMPLE 4and previously reported by Torres, Effects Of Modulus Of Elasticity OfCollagen Sponges On Their Cell-Mediated Contraction In Vitro (M.S.Thesis Massachusetts Institute of Technology, 1998)(on file with the MITLibrary). The cross-linking of the scaffolds is as described in EXAMPLE4 and as previously described by Torres, Effects Of Modulus OfElasticity Of Collagen Sponges On Their Cell-Mediated Contraction InVitro (M.S. Thesis Massachusetts Institute of Technology, 1998)(on filewith the MIT Library). The growth factors are added to the cell culturemedia as described in EXAMPLE 4. Culture, histology for analysis of cellmigration, DNA assay for cell proliferation, immunohistochemistry forthe contractile actin isoform, and SDS-PAGE analysis for the synthesisof type I collagen are as described in EXAMPLE 4. A pilot assay isperformed to assess the DNA content with the DHT cross-linked scaffoldwith the addition of no growth factors. Alternatively, a tritiatedthymidine assay can be evaluated or the specimens used for proliferationcan be fixed and serially sectioned, with sections at regular intervalsexamined for cell number density. Maximum number density is recorded foreach specimen type. Associated histology is used to estimate thepercentage of dead cells.

Example 15 Use of a Provisional Scaffold to Encourage TissueRegeneration

This EXAMPLE uses of a provisional scaffold to encourage tissueregeneration in the gap between the ends of the ruptured anteriorcruciate ligament without removal of the ligament. This has theadvantages of retaining the complex anterior cruciate ligament geometryand proprioceptive innervation of the ligament.

The objective of this EXAMPLE is to show the in vivo effect of placementof a provisional scaffold between the ruptured ends of the anteriorcruciate ligament. A rabbit model is chosen because of its previousestablishment as a mechanical and biochemical model for the humananterior cruciate ligament. We have previously shown that homologouscell distributions and vascularity between the human and lapine anteriorcruciate ligament (see, EXAMPLE 3). A CG scaffold is chosen as theprovisional scaffold, given its success in dermis and tendon and in thehuman anterior cruciate ligament in vitro model.

The goal of this EXAMPLE is to evaluate a novel method of treatment ofanterior cruciate ligament rupture which would facilitate ligamenthealing and regeneration after complete rupture. The potentialadvantages of regeneration over reconstruction include retention of thecomplex footprints of the human anterior cruciate ligament, preservationof the proprioceptive nerve endings within the anterior cruciateligament tissue, less invasive surgery with no graft harvest required,and maintenance of the complex fascicular structure of the anteriorcruciate ligament. Effective, minimally invasive, treatment of anteriorcruciate ligament rupture would be particularly beneficial to womenengaged in military training, as they are at an especially high risk forthis injury.

The problem to be investigated in this EXAMPLE is the development of animplant to be used for anterior cruciate ligament regeneration aftercomplete rupture of the ligament. Loss of the function of the anteriorcruciate ligament leads to pain, joint instability and swelling. Leftuntreated, a knee with instability secondary to anterior cruciateligament rupture leads to joint degeneration and osteoarthritis.

The objective of this EXAMPLE is to compare immediate primary repairwith primary repair and scaffold augmentation in the treatment ofanterior cruciate ligament rupture in a rabbit model. The technique ofprimary repair involves reapproximation of the ruptured ligament endswith sutures passed both through ligament and bone to stabilize thetissue. In this EXAMPLE, we determine whether cellular migration into agap between ruptured ligament fascicles if a provisional scaffold isprovided. Moreover, we determine what type of tissue is being depositedinto the gap between fascicles. The specific aim of this EXAMPLE is toevaluate the effect of a provisional collagen sponge-like implant tofacilitate anterior cruciate ligament regeneration of the ligament at 3weeks, 3 months, 6 months, and 1 year after injury, resulting in achange in the relative percentage of various tissue types in the defect.

Military Significance.

In a recent study of midshipmen attending the U.S. Naval Academy, theincidence rate of anterior cruciate ligament (ACL) injury was 10 timeshigher for women than men (Gwinn et al., Relative gender incidence ofanterior cruciate ligament injury at a military service academy[.], in66th Annual Meeting. Anaheim, Calif. (1999)). In military relatedtraining, the incidence of anterior cruciate ligament rupture was 6times higher that in competitive, high risk sports. The study also foundthat women engaged in military training sustained an anterior cruciateligament tear 3 times per every 1000 exposures. Thus, for women engagedin military training exercises twice a week, an average of 1 in 4 willsustain an anterior cruciate ligament tear each year (Gwinn et al.,Relative gender incidence of anterior cruciate ligament injury at amilitary service academy, in 66th Annual Meeting, Anaheim, Calif.(1999)). This study, and others, highlight the importance of anteriorcruciate ligament rupture in women, particularly women engaged inactivities which place them at risk for this injury, such as militarytraining. More than 200,000 people rupture their anterior cruciateligament annually (National Center for Health Statistics (1986)), andthe risk of anterior cruciate ligament rupture is significantly higherfor women engaged in intercollegiate sports when compared with theirmale counterparts (Arendt & Dick, 23(6) Am. J. Sports Med. 649-701(1995), Stevenson, 18 Iowa Orthop. J. 64-66 (1998)). For many womenathletes, anterior cruciate ligament rupture may be a career-endinginjury, as many patients can not return to their previous level ofactivity, even after repair or reconstruction (Marshall et al., 143 ClinOrthop 97-106 (1979); Noyes et al., 68B J. Bone Joint Surg. 1125-1136(1980)). Development of new methods of treatment of the rupturedanterior cruciate ligament, including ligament regeneration, may lead toquicker recovery times and improved rates of return to high levels ofphysical training for both women and men.

An anterior cruciate ligament rupture can be a devastating, if notcareer-ending, injury for women engaged in competitive athletics, and itis likely to be an event of similar magnitude in women in the militaryengaged in heavy physical activity. Currently, there is no reliabletreatment for anterior cruciate ligament rupture which has been shown toslow the progression of osteoarthritis in injured knees. Breakdown ofarticular cartilage is a source of pain and disability for many people.Left untreated, loss of anterior cruciate ligament function leads tomeniscal and chondral injury, and eventually can cause destruction ofthe entire joint, necessitating total joint replacement. Our biologicalimplant treats the defect in the ruptured anterior cruciate ligament.Such treatment may prevent the progression of joint deterioration seenin anterior cruciate ligament deficient knees, and in knees afteranterior cruciate ligament reconstruction. It provides a less invasivemethod of treatment for this common injury, and potentially retain thecomplex anatomy and innervation of the anterior cruciate ligament. Tofacilitate the continuance of women in physically demanding careers, anew method of treatment of anterior cruciate ligament rupture isnecessary, one which is minimally invasive, can restore the originalstructure and function of the anterior cruciate ligament, and has thepotential to minimize the progression to premature osteoarthritis.

Experimental Design and Rationale.

The following tests are provided to achieve the specific aim. TABLE 7shows the 3 test groups.

TABLE 7 Test Groups Number of Time to Group Knees Treatment Sacrifice I6 None 3 weeks I 6 None 3 months I 6 None 6 months I 6 None 12 months II6 Immediate Repair 3 weeks II 6 Immediate Repair 3 months II 6 ImmediateRepair 6 months II 6 Immediate Repair 12 months III 6 Immediate Repair +Scaffold 3 weeks III 6 Immediate Repair + Scaffold 3 months III 6Immediate Repair + Scaffold 6 months III 6 Immediate Repair + Scaffold12 months

Effect of a Collagen Implant on Immediate Primary Repair.

All animals have their anterior cruciate ligaments disrupted forcibly bypulling a suture through the ligament until it ruptures. After rupture,24 of the knees is closed without further treatment for the controlgroup. A second group of 24 knees undergoes immediate primary repairwith sutures and a third group of 24 undergoes primary repair with aprovisional scaffold placed in the defect between the ruptured ligamentends.

Power Calculation for Sample Size.

The power calculation for the sample size for the experimental groups isbased on detecting a 30% difference in the mean values of total fill,the area percentage of crimped collagenous tissue, and the values of thespecific mechanical properties. Assuming a 20% standard deviation, alevel of significance of α=0.05, for a power of 0.80 (β=0.20), 6specimens are required. We assume that a 30% change in the outcomevariable would be a meaningful indication of the benefit of onetreatment group over the other.

Collagen-Glycosaminoglycan (CG) Scaffold Synthesis.

The scaffold used in this EXAMPLE is the same scaffold used in EXAMPLE3. The 3-D culture substrate is a highly porous CG matrix, composed oftype I bovine hide collagen and chondroitin-6-sulfate. This is preparedby freeze-drying the collagen-glycosaminoglycan dispersion underspecific freezing conditions (Louie, Effect of a porouscollagen-glyosaminoglycan copolymer on early tendon healing in a novelanimal model (Ph.D. Thesis Massachusetts Institute of Technology1997)(on file with the MIT Library)). The average pore size of the CGscaffold manufactured in this manner is 100 μm.

Animal Model.

Mature female rabbits, weighing 3 to 5 kg, are used in this EXAMPLE.Prior to operation, the knee joints are examined roentgenographically toexclude animals with degenerative joint disease. All operations areperformed under general anesthesia and sterile conditions. A No. 5Ethibond suture is passed behind the anterior cruciate ligament and theligament ruptured in its proximal third by forcibly pulling the sutureforward while holding the knee immobilized. This mechanism of inducedrupture provides a more realistic, “mop-end” ruptured tissue thantransection with a blade. No attempt is made to debride the ligamentremnant of synovial tissue. Before closing the capsule, bleeding vesselsis clamped and cauterized. The knee joint is closed in layers. Animalshave surgery on only one limb to allow for protective weight bearing inthe post-op period. No post-operative immobilization is used.

The knees undergoing primary repair have a 2-0 Vicryl suture placedthrough each end of the ruptured ligament. The suture through the tibialremnant is then passed through the distal femur, and the suture throughthe femoral component passed through the tibia as described inMarshall's technique for primary repair (Marshall et al., 143 ClinOrthop 97-106 (1979).

Knees undergoing primary repair with the placement of the scaffold inthe defect between ruptured ligament ends have sutures placed in anidentical manner to that in the primary repair group. The CG scaffold isplaced into the defect prior to tensioning of the sutures.

Method of Histomorphometric Evaluation.

At the time of sacrifice, the skin is removed from the knee joint, andthe a capsulotomy performed on the lateral side of the knee, adjacent tothe patellar tendon, to allow adequate penetration of the joint by thefixative solution. After formalin fixation, the knee joints are immersedin 15% disodium ethylenediamine tetraacetate decalcifying solution, pH7.4. The specimens are placed on a shaker at 4° C. with three changes ofthe decalcifying solution each week for approximately four weeks.Samples are rinsed thoroughly, dehydrated, and embedded in paraffin at60 degrees Celsius. Seven-micrometer thick sections are stained withhematoxylin and eosin and Masson's trichrome. Selected paraffin sectionsare stained with antibodies to Type I and Type III collagen.

The specific tissue types filling the defect are determined byevaluating the percentage of the area of the central section through thedefect occupied by each tissue type: (1) dense, crimped collagenoustissue, (2) dense, unorganized collagenous tissue, (3) synovial tissue,and (4) no tissue. Cell number density, blood vessel density and nuclearmorphology of the fibroblasts are determined at each point along thelength of the ruptured ligament.

Radiographic Analysis.

All knees have anteroposterior and lateral x-rays taken pre-operativelyto assess for the presence of degenerative joint disease. Any animalsdemonstrating degenerative joint disease are disqualified from theanalysis. At the time of sacrifice, all knees are radiographed a secondtime to assess the development of radiographic changes consistent withdegenerative joint disease. Correlation between radiographic findingsand histologic changes in the articular cartilage of the knee is made.

Example 16 Testing of the Biological Implant of the Invention

The biologic replacement for fibrin clot for intra-articular use of theinvention is prepared and analyzed, such as is set forth in GuidanceDocument For Testing Biodegradable Polymer Implant Devices, Division ofGeneral and Restorative Devices, Center for Devices and RadiologicalHealth, U.S. Food and Drug Administration (Apr. 20, 1996) and DraftGuidance Document For the Preparation of Premarket Notification [510(K)]Applications For Orthopedic Devices. U.S. Food and Drug Administration(Jul. 16, 1997).

The composition and material structure (e.g., phases, reinforcement,matrix, coating) of the biologic replacement of the invention to beimplanted is characterized quantitatively. These analyses can includethe following:

Composition and Molecular Structure:

(a) main ingredients (such as collagen and glycosaminoglycan); (b) traceelements (e.g., heavy metals are low); (c) catalysts; (d) low molecularweight (MW) components (separate components which have and have notchemically reacted with the polymer, e.g., crosslinking agents); (e)polymer stereoregularity and monomer optical purity (if the monomer isoptically active; not applicable for collagen or glycosaminoglycan); (f)polydispersity, (g) number average molecular weight (M_(n)) (h) weightaverage molecular weight (M_(w)); (i) molecular weight distribution(MWD); (j) intrinsic (or inherent) viscosity (specify solvent,concentrations and temperature; not applicable for collagen orglycosaminoglycan); (k) whether the polymer is linear, crosslinked orbranched (l) copolymer conversion (e.g., block, random, graft; notapplicable for collagen or glycosaminoglycan); and (m) polymer blending.For the molecular weight, the inherent viscosity (logarithmic viscositynumber) or some other justifiable method (e.g., GPC) is measured priorto placement of samples in the physiological solution. Samples areremoved from immersion and loading at specified time periods throughoutthe duration of the test and tested for inherent viscosity. Dilutionratio in g/ml is noted.

Morphology (Supermolecular Structure):

(a) % crystallinity; (b) orientation of phases/macromolecules; and (c)types and amounts of phases.

Composite Structure:

(a) laminate structure; (b) thickness of each ply; (c) number of plies;(d) orientation and stacking sequence of plies; (e) symmetry of thelayup; (f) position of reinforcement within the matrix; (g) locationwithin the part; (h) 3 dimensional orientation; (i) fiber density (e.g.,distance between reinforcement components or reinforcement matrix volumeand weight ratios); (j) fiber contacts and cross-overs per mm; (k)reinforcement structure; (l) cross-sectional shape (m) surface textureand treatment; (n) dimensions; (o) fiber twist; (p) denier; (q) weave;(r) coating; (s) total number of coating layers; (t) thickness of eachlayer; (u) voids; (v) mean volume percent; (w) interconnections; (x)penetration depth and profile; and (y) drawing or photographs of theproduct illustrating the position of the coating and any variation incoating thickness (for example, see, FIGS.) The anatomical location andattachment mechanism for the biological implant of the invention isprovided in diagrams, illustrations, or photographs of the implant insitu.

Physical Properties:

(a) dimensional changes of the material as a function of time; (b)densities of reinforcement, matrix and composite; (c) mass of thesmallest and largest sizes; (d) roughness of all surfaces; (e) surfacearea of the smallest and largest sizes; (f) dimensioned engineeringdrawings of any nonrandom surface structure patterns (e.g., machinedstructures). Mechanical properties are important because they determinewhether the fracture site is adequately fixed to avoid loosening, motionand nonunion. Weight loss and inherent viscosity measurements may behelpful in screening different materials and in understandingdegradation mechanisms, though they may not directly address themechanical properties of the device. For weight loss testing, testsamples are weighed to an accuracy of 0.1% of the total sample weightprior to placement in the physiological solution. Upon completion of thespecified immersion/loading time, each sample is removed and dried to aconstant weight. Drying conditions may include enclosure in a desiccatorat standard temperature and pressure, use of a partial vacuum or the useof elevated temperatures. The weight is recorded to an accuracy of 0.1%of the original total sample weight. Elevated temperatures can be usedfor drying of the sample provided that the temperature used does notchange the sample (such as for collagen and glycosaminoglycan). Thedrying conditions used to achieve a constant weight are noted.

Thermal Properties (not Applicable for Collagen and Glycosaminoglycan):

(a) crystallization temperature; (b) glass transition temperature; and(c) melting temperature.

Strength Retention Testing.

In an in vitro degradation (or strength retention) test, samples areplaced under a load in a physiologic solution at 37° C. Samples areperiodically removed and tested for various material and mechanicalproperties at specified intervals (typically 1, 3, 6, 12, 26, 52, and104 weeks) until strength has dropped below 20% of the initial strength.

Various test solutions can be used. For example, bovine serum or PBSsolution in a volume at least 20 times the volume of the test sample maybe used. The pH of the solution approximates the pH of a physiologicenvironment (about 7.4). Samples are discarded if the measured pH isoutside the specified value of more than ±0.2. Each sampling containershould be sealable against solution loss by evaporation. Each testspecimen is kept in separate containers and isolated from otherspecimens to avoid cross contamination of degradation byproducts. Thesolution is kept sterile and properly buffered or changed periodically.

Samples are fully immersed in the physiological solution at 37° C. forthe specified period of time. One group of samples are stressed duringthe entire time in solution to simulate clinical worst case conditions,while another group of samples are set-up in the same environment,without stressing. The amount of sample agitation, solution flow pasttest specimens, frequency that the solution is replaced, and theclinical significance of these factors are recorded and analyzed.

In vitro degradation rates are compared to the in vivo degradation ratesso the in vitro test results can be extrapolated to clinical conditions.Samples are implanted in an animal model and mechanically tested todetermine if there are any significant difference in the outcome of testsamples degraded in vitro and in vivo. The degradation of the mechanicalproperties of the test device is compared to a device known in the art.The biological replacement of the invention is compared for thedetermination of substantial equivalence to a device such as is known inthe art (see, BACKGROUND OF THE INVENTION). A comparison of thesimilarities and differences of the known device to the biologicalreplacement of the invention is made in terms of design, materials,intended use, etc. Both devices are implanted either at the site ofactual loaded use (for example, the anterior cruciate ligament) or at anearby site. A range of healing time for the indicated repair isprovided from the literature (see, BACKGROUND OF THE INVENTION). Theimplantation time should be at least twice as long the longest time overwhich healing of the repair is expected to occur. Data for this set oftests may be from the same animals used in other tests.

For mechanical testing, the degradation of the mechanical properties ofthe biological replacement of the invention over time is compared to thesame changes for a device known in the art. The degradation values arevalidated to in vivo results. At time period throughout the duration ofthe immersion/loading time, samples are removed and tested. Samples aretested in a non-dried or ‘wet’ condition.

(8) Biocompatibility:

The biologic replacement of the invention is tested for biologicalresponse in an appropriate animal model. As part of the analysis, thedegradation by-products and their metabolic pathways are identified.

In vivo strength of repair studies compare the mechanical strength ofintact tissue to that of a tissue repaired using the biological implantof the invention or a device known in the art. A range of healing timesfor the indicated repair is provided from the literature (see,BACKGROUND OF THE INVENTION). The implantation time are at least twiceas long the longest time over which healing of the repair is expected tooccur. A histological analysis of biocompatibility at the implant sitedetermines the tissue response, normal and abnormal, to the presence ofthe biologic replacement of the invention and its breakdown products.The biologic replacement of the invention is implanted into an animalmodel such that it experiences loading.

(9) Sterilization Information:

See the Sterility Review Guidance. U.S. Food & Drug Administration (Jul.3, 1997). The sterilization method that was used [radiation, steam, EtO]is provided. If the sterilization method is radiation, then theradiation dose that was used is provided. If the sterilization method isEtO, then the maximum residual levels of ethylene oxide, ethylenechlorohydrin and ethylene glycol that were met is provided. These levelsare below those limits proposed in the Federal Register FR-27482 (Jun.23, 1978).

(10) Shelf Life:

The shelf-life of the final biologic replacement is determined.

Example 17 Human Anterior Cruciate Ligament Cell Growth in Acid-SolubleCollagen Hydrogel

The ability of cells of the human anterior cruciate ligament to survivein a collagen hydrogel was assesed. Human anterior cruciate ligament wasobtained from a patient undergoing total knee arthroplasty. The ligamentwas sectioned into 18 explants, each 1-2 mm on a side. The explants werethen cultured in a 6 well plate with 1.5 cc of media/well containinghigh-glucose DMEM, 10% FBS and antibiotics. Media were changed threetimes a week. After four weeks of culture, the tissue was removed andthe cells which had grown out of the tissue onto the plate weretrypsinized, counted (lx 10⁷ cells) and placed into two 75 cm² flasksovernight. On the second day, the gel components were assembled. Allingredients were kept on ice until placed into the molds. The molds weremade by cutting 6 mm ID silicon tubing into 1 inch lengths, then cuttingeach tube in half to make a trough. Silicon adhesive was then used tosecure a piece of polyethylene mesh to each end of the trough (FIG. 20).The adhesive was allowed to cure overnight, then sterilized by placinginto sterile 70% EtOH for 2 hours. The molds were exhaustively rinsed indIH20 and placed individually into 6 well plates prior to adding thegel. Prior to gel assembly, the cells were again trypsinized andcentrifuged. The media was aspirated, leaving a pellet of cells in a 15cc centrifuge tube. The gel was made by mixing 3.5 cc of acid-soluble,Type I collagen (Cell-A-Gen 0.5%, ICN Pharmaceuticals) with 1 cc of 10×Ham's F10, 1 cc of PCN/Strep, 0.1 ml Fungizone, 3 microliters of bFGFand 3.7 ml of sterile, distilled water. The above mixture was vortexed,and 1.4 ml of Matrigel added. The mixture was vortexed again, and then0.155 cc of 7.5% NaOH was added. The mixture was vortexed, and added tothe tube containing the cell pellet. The cells were resuspended in thecold gel by gentle mixing with a 1 cc pipette. The gel-cell mixture wasthen aliquoted into the molds, with 300 μl used in each mold. A drop ofthe gel-cell mixture was also placed into the bottom of each well tomonitor cell survival in the gel. The constructs were allowed to sit atroom temperature for 30 minutes, then moved to the 37 degree incubatorfor 30 minutes. After 1 hour, media containing 10% FBS was added tocover the mold and gel. Constructs were sacrificed for histology at 3hours, 3 days and 9 days. The gels were fixed in cold paraformaldehydefor 4 hours, then stored in PBS. The gels were embedded in paraffin and7 micrometer sections cut. Serial sections were stained with hematoxylinand eosin and Masson's trichrome.

On the second day of culture, the cells were noted to be growing in thegel on the bottom of each well, and in the gel constructs (using aninverted phase microscope). The gel had assumed an hourglass shape. Thisshape became more pronounced with time in culture. Staining of the gelsdemonstrated increasing cell numbers within the gel with time (FIG. 21),as well as increasing alignment of the cells along the longitudinal axisof the gel (with the cell processes pointing toward each end of theneo-ligament). By 9 days of culture, the gel constructs had a histologicappearance similar to that of the intact human ACL in terms of celldensity and alignment (FIG. 21).

These data demonstrate that acid-soluble collagen hydrogel is conduciveto ACL cell growth and proliferation.

Example 18 Human Anterior Cruciate Ligament Cell Mediated Contraction ofAcid-Soluble Collagen Hydrogel

The ability of endogenous or exogenous human anterior cruciate ligmentscells to mediate collagen hydrogel contraction was assessed. Human ACLexplants were cultured as in EXAMPLE 17 to obtain primary outgrowthhuman ACL cells. The cells were trypsinized from 9 wells (1.5 plates,approx 6×10⁶ cells), and collected in a pellet as in Experiment 1.Additional explants were obtained from the ACL of a second patientundergoing arthroplasty on Dec. 4, 2000 (the day before the experimentwas started.) Explants were 2 mm on each side. The explants werepredigested in 0.1% collagenase for 15 minutes at 37 degrees C. and thenrinsed exhaustively in sterile PBS and placed in culture media whichincluded 10% FBS. Explants were maintained in culture media at 37degrees C. and 5% CO2 overnight. The molds were made by sectioning the 6mm ID silicon tubing in half to make a trough, and sealing the ends ofthe trough with agarose, which was sterilized by autoclaving. Theagarose was melted by placing it in a 80 degree C. water bath, then 1drop was added to each end of the mold. The molds were sterilized byplacing in 70% EtOH for 2 hours, then rinsing exhaustively in sterileH2O. Each mold was placed into individual wells of a 6 well plate. Oneexplant was placed into each end of the trough (FIG. 22). A total of 18constructs were prepared. Each mold was able to hold 200 microliters ofliquid.

The gel was made by mixing 3.5 ml of acid-soluble Type I collagen(Cell-a-gen, 0.5%, ICN Pharmaceuticals), 1 ml of 10× Ham's F12, 1 ml ofPCN-Strep, 0.1 ml of Fungizone, 3 microliters of bFGF, 3.7 ml of ddIH20and 1.4 ml of Matrigel. The mixture was vortexed and 0.155 cc of NaOHadded. The mixture was vortexed again and 5 cc added to the cell pellet.The cells were resuspended in 5 cc of the gel, and the remaining 5 ccwere reserved for the cell-free gel constructs. Nine constructs weremade using the gel with added cells (C group), and nine were made withthe cell-free gel (CF group). The explants and gel were cultured for 21days. Media were changed three times a week, with measurements of thedistance between the explants made at each media change. Constructs ineach group were sacrificed for histology at days 0, 3, 7, 14 and 21. Theconstructs used for histology were fixed in 10% neutral bufferedformalin for one week, then embedded in paraffin and sectioned at 7micrometers. Serial sections were stained with hematoxylin and eosin toevaluate cell density and alignment.

On day one, the cells were seen in the gel of the cell-gel group, andthe gels in this group were noted to already be contracting and drawingthe two pieces of ligament tissue closer together (FIG. 23). No cells inthe gel, or contraction of the gel was noted in the cell-free group,until 3 days after culture, and at 7 days, cells were seen near theexplants in all of the gels in the cell-free group. Contraction of thegels was noted to begin at 7 days after culture in the cell free group(FIG. 23). The histologic analysis demonstrated increasing numbers ofcells in both the cell gel and the cell free gel. The increase in thecell-seeded gel may have been due to the proliferation of the seededcells, or to the migration of cells from the tissue into the gel. Theincrease in the cell-free gel was from migration of cells from theligament tissue. By day 21, the cell density in the two groups wassimilar (FIG. 24).

Cell mediated contraction of the collagen gel is seen whether the cellsare seeded into the gel, or whether they migrate in from adjacenttissue. The cell-free gel has a similar density of cells at theinterface after three weeks in culture with the ACL explants.

Example 19 Platelet Rich Plasma Enhanced Adhesive Properties of theCollagen Hydrogel

To determine the ability of platelet rich plasma to enhance the adhesiveproperties of the collagen hydrogel four experimental groups weretested.

The four groups tested were:

1. Explant (no predigestion) and gel without cells

2. Explant (collagenase predigestion) and gel without cells

3. Explant (no predigestion) and gel with fibroblasts added

4. Explant (no predigestion) and gel with platelet rich plasma added

For each group, an explant was secured at one end of a mold, andpolyethylene mesh at the other end. Groups 1, 3 and 4 were cultured for4 days as in EXAMPLE 18. Group 3 was predigested in 0.1% collagenase for10 minutes at 37 degrees C., washed in PBS and cultured.

To fasten the tissue to the mold, 6 well plates were coated withSylgard. After the Sylgard cured overnight, the wells were sterilizedwith 70% EtOH for two hours and exhaustively rinsed. The molds were madewith silicon adhesive used to secure polyethylene mesh to one end of thetrough and then sterilized, as in experiment 1. Each mold was placedinto an individual well of a 6-well plate. On the other end of thetrough, a 30 gauge needle was placed through the explant, through themold wall and into the Sylgard to secure the tissue within the mold(FIG. 25). Once the constructs had been made, the three gels wereassembled.

For the gel without cells (groups 1 and 2), the gel was prepared as inEXAMPLE 17 and 18. A sterile pipette was used to add 300 microliters ofgel to each mold.

For the fibroblast gel (group 3), we trypsinized cells from two 75 cm²flasks and resuspended these cells in 10 cc of gel prepared as inEXAMPLE 17 and 18

For the platelet rich plasma (PRP) group, two 4.5 cc tubes of blood weredrawn from the antecubital vein of a volunteer donor into blue top tubescontaining 3.2% Sodium Citrate. The tubes were spun at 700 rpm for 20minutes. After spinning, 1.4 cc of the platelet-rich plasma upper layerwas aspirated from each tube and placed into a sterile microcentrifugetube. All tubes were stored in the 37 deg C. incubator until use. A 15microliter aliquot of the PRP was taken and the platelet and WBC densitycounted. A density of 1.6×10⁸ platelets/ml was determined. Fewer than4×10³ WBCs/ml were found. For the PRP gel, the collagen, PCN/strep, bFGFand Matrigel were mixed. Next, 0.25 ml of 10× Ham's F12 was added to 2.5cc of this mixture and vortexed. The PRP (1.4 ml at 37 deg C.) was addedto the gel components, 0.077 ml of 7.5% NaOH added and the mixturepipetted to mix. The resultant gel was added to each mold for the PRPgroup.

The gels were allowed to set for 30 minutes and then 5 cc of mediacontaining 10% FBS was added to each well. Media were changed threetimes each week. The minimum width of the gels was measured weekly as anestimate of cell-mediated contraction. Constructs from each group weresacrificed for histology at 3 hours, two days, two weeks, three weeksand four weeks of culture. The gel containing the PRP (group 4)demonstrated the fastest set time at setting beginning at 5 minutes, andthe gel becoming so thick by 10 minutes that it was impossible topipette. All gels contracted throughout the experiment (FIG. 26), withthe fibroblast seeded gel contracting to the smallest width. However,the fibroblast seeded gel released from the tissue interface at 3 weeks,where the other groups maintained contact throughout the experiment.

The PRP gel (group 4) demonstrated the greatest contractile potentialwithout releasing from the tissue, suggesting a stronger adhesiveproperty than the fibroblast seeded gel. The histology at two weeksdemonstrated the highest cell numbers in groups 1 and 4 (FIG. 27). Thus,the addition of the PRP component did not deter cell migration into thegel. The cells maintained an elongated morphology.

In summary, the PRP and standard hydrogel are similar in encouragingcell ingrowth from surrounding tissue. The PRP gel contracted to agreater extent than the standard hydrogel. The PRP maintained betteradhesion to the tissue than the fibroblast seeded gel.

Example 20 Resiliency of Platelet Rich Plasma Collagen Hydrogels

The resiliency of the platelet rich plasma collagen hydrogels wereassessed using a cyclic stretching machine. Explants were made as inEXAMPLES 17 and 18. The explants were connected by a 3-0 nylon sutureloop to prevent excessive tension in the gels. The explants were placedinto molds, as in EXAMPLE 18, and the gap between filled with either thegel used in experiments EXAMPLES 17 and 18 (standard gel) or the PRP gelof EXAMPLE 19. Eight constructs were used in each group. After thestandard gel had been added to the constructs, it was allowed to set upfor 60 minutes at room temperature and media added. For the PRP group,the gel was allowed to set up for 30 minutes at room temperature. Aftersetting, the constructs were transferred into a cyclic stretchingmachine and cultured for 18 days.

The standard gels all dissolved with motion through the media,suggesting they were not strong enough to resist fluid flow after evenone hour at room temperature. In the PRP gel group, 6 of the 8constructs maintained continuity between explant-PRP gel-explant andwere placed into the cycling apparatus. All six constructs maintainedcontact throughout the 18 days of culture. When removed from theculture, the PRP gel was stretchy and resilient. Thus, the PRP gel issuperior to standard hydrogels in resisting dissolution by fluid flow.

Example 21 Effect of Platlet Rich Plasma and Matrigel on CollagenHydrogel

To determine the optimal concentration of PRP and matrigel to use in thecollagen hydrogel gel without altering the cell proliferation rates orcollagen production rate the following experiments were conducted.Primary outgrowth cells were obtained from one patient undergoing TKR asin EXAMPLE 17. Constructs were made as in EXAMPLE 17. One of five typesof gel were added to the molds. The five gel groups were

-   -   1. Collagen Hydrogel (standard as used in Expts 1, 2, 3 and        4—contains Matrigel)    -   2. Group 1+15% PRP    -   3. Group 1+30% PRP    -   4. Group 1+45% PRP    -   5. Group 3 without Matrigel

Twenty constructs for each group were cultured and four sacrificed at 2hours, 1 day, 1 week, 2 weeks and 3 weeks of culture. One construct foreach group at each time point was reserved for histology, and the otherthree labeled with tritiated thymidine (to measure cell proliferation)and 14C proline (to measure collagen production) for 24 hours prior tosacrifice. Minimum gel width was measured each week for all constructs.

Example 22 Treatment of Partial ACL Tears In Vivo

Canine ACLs are visualized after routine mini-arthrotomy medial to thepatellar tendon and sharply transected with a 3.5 mm beaver bladecentrally near the tibial insertion. The partial transection doesn'tdestabilize the knee and leaves the ACL fibers intact around the centraldefect. The collagen glue, or no treatment, is placed in the tear. Thecollagen based glue is prepared by mixing acidic type I collagen with aspecified cocktail of growth factors and extracellular matrix proteinsoptimized for ACL cells. Gelling will be accomplished by neutralizingthe pH with NaOH and warming the mixture to room temperature. 2.5 cc ofgel is injected into each experimental transection site.

In the right knee of each animal, the collagen glue without growthfactors is placed in partial ACL tear and in the left knee, thecollagen-based glue containing supplemental growth factors is introducedinto partial ACL tear. The knee is closed in a routine fashion.

Animals are allowed free activity once they have awoken from anesthesia.

The dogs are either sacrificed at 10 days, three weeks and six weeks.Ligaments are sharply dissected from their bony insertion sites andfixed in formalin.

After fixation, specimens are embedded in paraffin and longitudinalsections, 7 μm thick, are microtomed and fixed onto glass slides.Representative longitudinal sections microtomed from each ligament arestained with hematoxylin and eosin for cell counting and with antibodiesto α-SM actin. In situ hybridization for type I and III collagen is alsoperformed.

The α-SM actin isoform is detected by immunohistochemistry using amonoclonal antibody (Sigma Chemical, St Louis, Mo., USA).Deparaffinized, hydrated slides are digested with 0.1% trypsin (SigmaChemical, St. Louis, Mo., USA) for twenty minutes. Endogenous peroxideis quenched with 3% hydrogen peroxide for 5 minutes. Nonspecific siteswill be blocked using 20% goat serum for 30 minutes. The sections arethen incubated with mouse monoclonal antibody to α-SM actin (SigmaChemical, St. Louis, Mo., USA) for one hour at room temperature.Negative controls are incubated with non-immune mouse serum diluted tothe same protein content. The sections are then incubated with abiotinylated goat anti-mouse IgG secondary antibody for 30 minutesfollowed by thirty minutes of incubation with affinity purified avidin.The labeling is developed using the AEC chromagen kit (Sigma Chemical,St Louis, Mo.) for ten minutes. Counterstaining with Mayer's hematoxylinfor 20 minutes will be followed by a 20 minute tap water wash andcoverslipping with warmed glycerol gelatin.

Following 24 hour fixation of the tissue in 4% paraformaldehyde at 4°C., the tissue to be used for in situ hybridization is dehydrated,embedded in paraffin, sectioned at 6 μm, and placed on slides. Thetissue is deparaffinized in xylene, hydrated in ethanol, and washed inphosphate buffered saline. The tissue sections is fixed with 4%paraformaldehyde at 25° C. for 20 minutes, digested with proteinase K(20 mg/ml) (Sigma Chemical, St Louis, Mo., USA) at 37° C., thenpost-fixed in 4% formaldehyde (Fluka A. G., Buchs, Switzerland). Probesfor type-I collagen will be labeled with[32P]deoxycytidine-5-triphosphate (Dupont, Wilmington, Del., USA) byrandom priming to a specific activity of 0.5−1.5×107 cpm/μg of DNA(Stratagene, La Jolla, Calif., USA). The tissue is hybridized for 20hours at 42° C., and the slides passed through a series of stringencywashes at 37 deg C. for 15 minutes. After dehydration in gradedethanols, the slides are dipped in Ifford K5 emulsion (Polysciences,Warrington, Pa., USA) and exposed for 21 days at 4 deg C. The slides aredeveloped in D19 developer (Eastman Kodak, Rochester, N.Y., USA) andfixed at 15 deg C. Subsequently, the sections are stained with toluidineblue and analyzed and photographed under bright and dark fieldillumination. For each set of slides, a negative control(pSPT19-neomycin) are used. Relative matrix synthetic activity (type Icollagen) within the ligaments are graded by a blinded observer from 1+to 4+ and further divided by spatial localization of activity.

Histological slides are examined using a Vanox-T AH-2 microscope(Olympus, Tokyo, Japan) with normal and polarized light as previouslydescribed (4). Briefly, sections are examined at 2 mm intervals,beginning distal to the femoral insertion site and ending proximal tothe tibial insertion site, along the length of fascicles of theanteromedial bundle of each ligament. At each location, 3 0.1 mm² areasare analyzed for cell number density, and nuclear morphology. At eachlongitudinal location, the number of crossing vessels will be divided bythe width of the section at that location to estimate a blood vesseldensity. The cell morphology is classified based on nuclear shape:fusiform, ovoid or spheroid. Fibroblasts with nuclei with aspect ratiosgreater than 10 will be classified as fusiform, those with aspect ratiosbetween 5 and 10 as ovoid, and those with nuclear aspect ratios lessthan 5 as spheroid. At each location, the total number of cells iscounted and divided by the area of analysis to yield a cell density, orcellularity. Cell morphology is mapped for the longitudinal sections andthe course of the blood vessels through the section noted.

Smooth muscle cells surrounding vessels are used as internal positivecontrols for determination of α-SM actin-positive cells. Negativecontrol sections, substituting diluted mouse serum for the primaryantibody, will be prepared on each microscope slide to monitor fornonspecific staining. Positive cells will be those that demonstratechromogen intensity similar to that seen in the smooth muscle cells onthe same microscope slide and that had significantly more intense stainthan the perivascular cells on the negative control section. Any cellwith a questionable intensity of stain (e.g., light pink tint) is notcounted as positive. The α-SM actin-positive cell density isreported asthe number of stained cells divided by the area of analysis and thepercentage of α-SM actin-positive cells is determined by dividing thenumber of stained cells by the total number of cells in a particularhistologic zone.

Polarized light microscopy is used to aid in defining the borders offascicles and in visualizing the crimp within the fascicles. Measurementof the crimp length is performed using a calibrated scale underpolarized light.

Analysis of variance (ANOVA) is performed using statistical software(Statview Version 5.0, SAS Institute, Inc., Cary, N.C., USA). One-factorANOVA is used to determine the significance of location on thehistological parameters for each experimental group individually, andtwo-factor ANOVA is used to determine the significance of experimentalgroup and location on the histological parameters. Fisher's protectedleast squares difference (PLSD) is used to determine the significance ofdifferences between groups. The level of significance is set at 95%(p<0.05). The data is presented as the mean±the standard error of themean.

Example 23 Effect of the Addition of Insoluble Type I Collagen Fibers tothe Soluble Growth Factor Gel on Gel Viscosity Cellular Proliferation,Cellular Collagen Production in the Gel and Cellular Migration

Standard growth factor gel is made by mixing 14 cc of acid-soluble, TypeI collagen (Cell-A-Gen 0.5%, ICN Pharmaceuticals) with 4 cc of 10× Ham'sF10, 4 cc of PCN/Strep, 0.4 ml Fungizone, and 5.4 ml of sterile,distilled water. 6 ml of growth factor cocktail containing FGF-2, TGF-βand PDGF-AB is added to the gel. The above mixture is vortexed, and 6 mlof Matrigel (Becton Dickinson) added. The mixture is vortexed again, andthen 0.625 cc of 7.5% NaOH is added to neutralize the gel. The gel iskept on ice until use. The 40 cc of standard gel is divided into four 10ml aliquots. One of the aliquots is reserved for use with no addedinsoluble Type I collagen (control). The remaining three aliquots haveeither 0.01 mg, 0.1 mg or 1 mg of insoluble Type I collagen (IntegraLife Sciences, Plainsboro, N.J.) added to each tube and vortexed to mix.

Gel viscosity is determined using a AR1000 controlled stress rheometer(TA Instruments, New Castle, Del.), Rheology Advantage Software (TAInstruments, New Castle, Del.), and a cone and plate geometry. Therheometer is calibrated daily to ensure accuracy. The calibration isperformed by comparing the measured viscosity of Cannon CertifiedViscosity Standard Mineral Oil to its actual value through the range of12 Pa to 5 Pa, correcting for temperature variation. The ratio of thegiven value to the measured value was multiplied by all viscosityresults obtained until the next calibration. Previous experiments haveshown the calibration ratio to fall within 20% of unity.

Once the calibration is performed, 1.7 ml of the gel to be tested ispoured onto the lower plate of the rheometer, which is then raised towithin 28 micrometers of the upper plate. Within 30 seconds of gelplacement in the rheometer, a fixed torque is applied to the movablecone, resulting in a shear stress that is proportional to the shearstrain applied to the fluid. The rheometer measures the steady-stateangular velocity of the movable cone. The angular velocity isproportional to the strain rate. The rheology software performs thesecomputations and computes the shear stress and strain rate. Theviscosity is measured at a shear stress of 1 Pa. Gel samples are run intriplicate.

ACL cell proliferation and collagen production in the gel is measured asfollows.

Human anterior cruciate ligament remnant is obtained from a patientundergoing ACL reconstruction. The ligament is sectioned into 18explants, each 1-2 mm on a side. The explants are then cultured in a 6well plate with 1.5 cc of media/well containing high-glucose DMEM, 10%FBS and antibiotics. Media is changed three times a week. After fourweeks of culture, the tissue is removed and the cells that grow out ofthe tissue onto the plate is trypsinized, counted and placed into 2 75cm² flasks overnight. Prior to gel assembly, the cells are trypsinizedand centrifuged. The cells are resuspended in 10 cc of DMEM, counted anddivided into 4 equal aliquots of 1×10⁷ cells each. Each aliquot isre-centrifuged and the media is aspirated, leaving a pellet of cells ina 15 cc centrifuge tube.

ACL cell proliferation and collagen production is determined as follows.Experimental constructs are formed using molds made by cutting 6 mm IDsilicon tubing into 1″ lengths, then cutting each tube in half to make atrough. Silicon adhesive is used to secure a piece of polyethylene meshto each end of the trough. The adhesive is allowed to cure overnight,then sterilized by placing into sterile 70% EtOH for 2 hours. The moldsare exhaustively rinsed in dIH₂0 and placed individually into 6-wellplates prior to adding the gel.

Gels are prepared as above. Each gel is added to a different 15 cc tubecontaining a pellet of 1×10⁷ ACL cells. The cells are resuspended in thecold gel by gentle mixing with a 1 cc pipette. The gel-cell mixture isthen aliquoted into the molds, with 300 μl used in each mold. A drop ofthe gel-cell mixture is also placed into the bottom of each well tomonitor cell survival in the gel. The constructs are allowed to sit atroom temperature for 30 minutes, then moved to the 37° C. incubator for30 minutes. After 1 hour, media containing 10% FBS is added to cover themold and gel. The cell constructs are cultured at 37° C. and 5% CO2 withmedia changes three times a week.

At 1 day, 1 week, 2 weeks and 3 weeks of culture, radiolabelling todetermine rates of cell proliferation and collagen production isperformed. At each time point, three constructs from each group (12constructs/time point) is radiolabeled with [³H] thymidine and [¹⁴C]proline. The media is changed and 2 μCI/ml [³H] thymidine and 2 μCi/mlof [¹⁴C] proline is added to the fresh media in each well. After 24hours, the media will be removed and the constructs rinsed four times incold phosphate buffered saline. The gels are placed into separatemicrocentrifuge tubes and stored at −70° C. The gels are defrosted anddigested individually in 1 ml of 0.5% papain/buffer solution (SigmaChemical, St Louis, Mo., USA) in a 65° C. water bath, and aliquots ofeach used for the biochemistry assays.

In order to determine the rates of DNA proliferation and collagensynthesis, a 100 μl aliquot is taken from each of the 96 samples andplaced into a scintillation vial with 4 cc of scintillation fluid(Fisher Scientific, Chicago, Ill., USA). All samples are counted using aliquid scintillation counter (Tri-Carb 4000 Series, Liquid ScintillationSystems, Model 4640) for both [³H] and [¹⁴C] with compensation for thebeta emission overlap accounted for in the analysis software with a duallabel counting program. For anterior cruciate ligament cells, it hasbeen previously demonstrated that 24 to 25% of the uptake of [¹⁴C]proline is in collagen production, using a modified method ofPeterkofsky and Diegelmann. The final wash is also analyzed to ensure itcontains less than 0.001% of the radioactivity of the original labelingmedia.

For DNA analysis, a 500 μL aliquot of the digestis combined with 50microliters of Hoechst dye no. 33258 and 1 ml of a filteredTris-EDTA-NaCL buffer solution at pH 7.4 and evaluated fluorometrically.The results are extrapolated from a standard curve using calf thymus DNA(Sigma Chemical, St Louis, Mo., USA). Negative control specimensconsisting of the gel alone is also assayed to assess background fromthe scaffold.

The counts per minute readings for the proliferation and collagenproduction assays are individually normalized by the DNA content of eachsample to give a cell-based proliferation and collagen production rate.These data is used in the statistical analyses. Analysis of variance(ANOVA) is used to determine the statistical significance of theaddition of growth factor and time on the histologic and biochemicalmarkers of cell behavior, with Fisher's protected least squaresdifference used to determine statistical significance of differencesbetween individual groups.

Cellular migration from ACL tissue into the gel is determined usingruptured ACL tissue obtained from patients undergoing ACLreconstruction. The ligaments are sectioned into explants measuring 2 mmon each side. The explants are rinsed exhaustively in sterile PBS andplaced in culture media which includes 10% FBS. Explants are maintainedin culture media at 37° C. and 5% CO2 overnight. Molds are made bysectioning the 6 mm ID silicon tubing in half to make a trough, andsealing the ends of the trough with agarose, which will be sterilized byautoclaving. The agarose will be melted by placing it in an 80° C. waterbath, and then 1 drop is added to each end of the mold. The molds aresterilized by placing in 70% EtOH for 2 hours, then rinsing exhaustivelyin sterile H₂O. Each mold is placed into individual wells of a 6 wellplate. One explant is placed into each end of the trough. Each moldholds 200 microliters of liquid. The same four groups of gels asdescribed above are used. The explants and gel will be cultured for 21days. Media will be changed three times a week. Constructs in each groupare sacrificed for histology at days 0, 3, 7, 14 and 21. The constructsused for histology are fixed in 10% neutral buffered formalin for oneweek, then embedded in paraffin and sectioned at 7 micrometers. Serialsections are stained with hematoxylin and eosin to evaluate cell densityand alignment. Cell density is measured in four 0.1 mm² areas at fourlocations relative to the tissue/gel interface to determine cell densityas a function of location from the tissue. The maximal migrationdistance within the gel will also be measured for each construct. Twofactor ANOVA for gel group and time in culture will be performed todetermine the significance of the effect of the fiber reinforcement oncellular density and migration distance.

Example 24 Effect of Increased Construct Viscosity on Gel Retention inthe ACL Defect in an Ex Vivo Model

The effect of increased construct viscosity on gel retention in the ACLdefect is determined using canine knees obtained at the time ofsacrifice. All knees have partial transections in the ACL. Knees aretreated with the control gel, or gels containing increasing amounts ofinsoluble collagen fiber. The degree of gel retention is assessed bothgrossly and histologically. To expose the ACL, a paramedian arthrotomyalong the medial border of the patellar tendon is made. The fat pad isswept laterally to expose the ACL. A partial defect is made in the ACLusing a transverse cut. After preparation of the defect, the gelcomponents will be mixed as described in EXAMPLE 23.

After preparation of the gels, 100 microliters of the control gel isadded to three of the prepared defects. The gel is allowed to set for 10minutes prior to closure of the knee. This procedure is repeated in 12knees, using each of the four gel types in three knees. Skin closure isreapproximated using a towel clamp and the knee allowed to rest for 1hour. After 1 hour has elapsed, the knee is re-opened and the ACLresected sharply from its tibial and femoral insertion sites using an 11blade.

The ACL is fixed for 24 hours in fresh paraformaldehyde and embedded inparaffin. The twelve ligaments are sectioned longitudinally and serialsections analyzed for degree of filling by the four different gels. AMasson's Trichrome stain will be used to differentiate between the geland surrounding tissue. The total area of the ligament defect will bemeasured using a calibrated reticule and the total area of fillingmeasured using the same device. The percentage of filling in 4 sectionswill be determined and averaged for each specimen. One factor ANOVA forgel type will be used to determine the significance of the effect of geltype on percentage defect filling.

Example 25 Effect of Implanting a Reinforced Growth Factor Gel into aPartially Transected ACL on In Vivo Tissue Stimulation

A partial ACL transection model will be used for this experiment. Inthis model, no spontaneous healing of the defect (as measured by grossappearance of defect and mechanical properties) is noted withouttreatment. Twelve dogs are used, with each dog having gel alone placedinto the defect on one limb (control), while the fiber-reinforced growthfactor gel is placed into the defect on the opposite limb. Three dogsare sacrificed at day 0, day 10, week 3 and week 6.

Gel Preparation

The control gel (no added insoluble Type I collagen) and the gel withthe concentration of insoluble Type I collagen are used in thisexperiment. To make both gels, all ingredients are kept on ice untilplaced into the knee. The standard gel is made by mixing 3.5 cc ofacid-soluble, Type I collagen (Cell-A-Gen 0.5%, ICN Pharmaceuticals)with 1 cc of 10× Ham's F10, 1 cc of PCN/Strep, 0.1 ml Fungizone, and 1.4ml of sterile, distilled water. 1.5 ml of growth factor cocktailcontaining FGF-2, TGF-β and PDGF-AB is added to the gel. The abovemixture is vortexed, and 1.4 ml of Matrigel added. The mixture isvortexed again, and then 0.155 cc of 7.5% NaOH is added to neutralizethe gel. The fiber-reinforced gel is made by mixing a standard gel, thenadding the optimized weight of collagen and vortexing to mix.

Surgical Procedure

For each animal, both knees are exposed. As this procedure does notresult in instability of the knee, or require knee immobilization, bothknees can be used in each animal. On one side, the fiber reinforced gelis placed into the defect, while of the contralateral side, gel withoutinsoluble Type I collagen is used. To expose the ACL, a 2 cm incision ismade along medial border of patellar tendon using a 15 blade. Theparatenon is released along the medial edge of the tendon. The fat padis incised and retracted laterally. Hemostasis is achieved prior toproceeding. A partial defect is made in the ACL and filled with controlor fiber-reinforced gel. The tissues is maintained in retraction for 10minutes and the knees closed using 3-0 PDS in a subcutaneous layer aswell as a subcuticular closure with running 3-0 PDS. Dogs are keptcomfortable in the post-operative period with narcotic medication. Nonon-steroidal anti-inflammatory medications is nused. Antibiotics aregiven for 48 hours post-operatively. At 10 days from gel placement,three dogs are sacrificed. The ACLs are sharply resected from theirtibial and femoral attachments and placed into fresh 4% paraformaldehydefor 24 hours prior to paraffin embedding. Three additional dogs aresacrificed at 3 weeks and 6 weeks, and the ligaments fixed inparaformaldehyde. Histologic analysis are performed to determine %filling of defect and rate of cell migration into the gel from thesurrounding tissue.

Rates of Cellular Migration from the ACL Tissue into the Defect

All ligaments are fixed in cold 4% paraformaldehyde for twenty-fourhours, embedded in paraffin and sectioned into 7 micrometer sections.Sections are taken in the sagittal plane to allow for evaluation of thegel in the rupture site and sites 1, 2, 3 and 5 mm from the rupturesite. Hematoxylin and eosin and Masson's Trichrome staining is performedto facilitate light microscopy examination of cell morphology anddensity in the five zones. The cell number density within the gel willbe measured in 5 distinct 0.1 mm² fields and the results averaged andmultiplied by 10 to determine the average cell number density within thegel per mm². Two factor ANOVA is used to determine the significance offiber reinforcement and time on the cell number density within the gel.

Cell Number Density and Vascularity in the Adjacent Tissue

Histologic parameters of cell number density and nuclear morphology ismeasured in each histologic zone. The tissue adjacent to the defect isanalyzed histomorphometrically as a function of distance from therupture site. The cell number density, blood vessel density, density ofmyofibroblasts and nuclear morphology is assessed at each site. Thedensity of blood vessels and myofibroblasts are facilitated by the useof immunohistochemistry for alpha-smooth muscle actin (see protocolbelow). Plots of the cell number density and blood vessel density, as afunction of distance from the growth factor gel site are plotted toillustrate increases in cell number density adjacent to the rupturesite. Sections are also analyzed for depth of proteoglycan loss,fascicular fissuring, and synovial loss. Cells that display a pyknoticnucleus and either shrunken, deeply eosinophilic cytoplasm orfragmentation of the nucleus/cytoplasm are counted as apoptotic usinghistologic criteria. Two factor ANOVA is used to determine thesignificance of the addition of fiber reinforcement and time on the cellnumber density, blood vessel density, myofibroblast density and nuclearmorphology in the surrounding tissue.

Immunohistochemistry Protocol

Immunohistochemistry for alpha-smooth muscle actin (SMA, marker formyofibroblasts and perivascular cells) is performed as previouslyreported by our laboratory^(22,23,25). In the immunohistochemicalprocedure, deparaffinized, hydrated slides is digested with 0.1% trypsin(Sigma Chemical, St. Louis, Mo., USA) for twenty minutes. Endogenousperoxidase is quenched with 3% hydrogen peroxide for five minutes.Nonspecific sites are blocked using 20% goat serum for thirty minutes.The sections are incubated with the mouse monoclonal antibody to SMA forone hour at room temperature. A negative control section on eachmicroscope slide is incubated with non-immune mouse serum diluted to thesame protein content, instead of the SMA antibody, to monitor fornon-specific staining. The sections are incubated with a biotinylatedgoat anti-mouse IgG secondary antibody for thirty minutes followed bythirty minutes of incubation with affinity purified avidin. The labelingis developed using the AEC chromogen kit (Sigma Chemical, St Louis, Mo.)for ten minutes. Counterstaining with Mayer's hematoxylin for twentyminutes is followed by a twenty-minute tap water wash and coverslippingwith warmed glycerol gelatin.

Example 26 Effects of the Addition of Growth Factors on theFibroinductive Properties of a Collagen Scaffold

The effect of growth factors to stimulate human ACL cell migration,proliferation, and collagen production was assessed.

Six human ACLs were divided into explants, and the tissue placed intoculture with a CG scaffold. Explant/scaffold constructs were culturedwith either 2% FBS (control), or 2% FBS supplemented with one of thefollowing: EGF, FGF-2, TGF-β1 or PDGF-AB. Histologic cell distribution,total DNA content, proliferation rate and rate of collagen synthesiswere determined at two, three and four weeks.

The ACL cells cultured with EGF and FGF-2 demonstrated a more uniformdistribution of cells in the scaffold than the other groups, as well ashigher numbers of cells by DNA analysis at the two-week time point.Scaffolds cultured with FGF-2, TGF-β1 or PDGF-AB demonstrated increasedrates of cell proliferation (FIG. 4) and collagen production whencompared with controls.

These results suggested that certain growth factors can differentiallyalter the biologic functions of human ACL cells in a collagen matriximplanted as a bridging scaffold at the site of an ACL rupture. Based onthese findings, the addition of FGF-2, TGF-β1 or PDGF-AB to animplantable collagen scaffold may facilitate ligament regeneration inthe gap between the ruptured ends of the human ACL.

Example 27 Survival of Human Anterior Cruciate Ligament Cells in FGF-2Supplemented Collagen Gel

The survival of human anterior cruciate ligament cells in a collagen gelsupplemented with FGF-2 was assessed.

Primary outgrowth ACL cells were obtained from explant cultures. Thecells were added to a collagen gel containing FGF-2, and the cell-gelmixture placed into silicon molds between two pieces of openpolyethylene mesh. Constructs were sacrificed for histology at 3 hours,3 days and 9 days.

The number of cells in the gel increased with time in culture. By 9 daysof culture, the gel constructs had a histologic appearance similar tothat of the intact human ACL in terms of cell density and alignment(FIG. 29). The acid-soluble collagen hydrogel with FGF-2 is conducive tohuman ACL cell growth and proliferation.

Example 28 Migration of Human Anterior Cruciate Ligament Cells in FGF-2Supplemented Collagen Gel

The migration of human anterior cruciate ligament cells in a collagengel supplemented with FGF-2 was assessed.

Explants were placed at each end of a mold and the mold filled with anacellular collagen gel (n=9) or a gel containing ACL fibroblasts (n=9)Constructs in each group were sacrificed for histology at days 0, 3, 7,14 and 21.

The histologic analysis demonstrated increasing numbers of cells in boththe cell gel and the cell free gel. The increase in the cell-seeded gelmay have been due to the proliferation of the seeded cells, or to themigration of cells from the tissue into the gel. The initial increase inthe cell-free gel was from migration of cells from the ligament tissue.By day 21, the cell density in the two groups was similar. ACL cellswill migrate from the tissue into an adjacent collagen gel withcontaining FGF-2, resulting in similar cell number densities to acell-seeded gel by three weeks of culture.

Example 29 Determination of the Optimal Concentration of “Growth FactorCocktail” (GFC) to Use in the Gel for Maximum Stimulation of CellProliferation and Collagen Production

Primary outgrowth cells were obtained from one patient undergoing TKR.Constructs were made as described in EXAMPLE 27 and 28. One of fourtypes of gel were added to the molds. The four gel groups were

1. Collagen Hydrogel with FGF-2 only

2. Group 1+15% GFC

3. Group 1+30% GFC

4. Group 1+45% GFC

Twenty constructs for each group were cultured and four sacrificed at 2hours, 1 day, 1 week, 2 weeks and 3 weeks of culture. One construct foreach group at each time point was reserved for histology, and the otherthree labeled with tritiated thymidine (to measure cell proliferation)and 14C proline (to measure collagen production) for 24 hours prior tosacrifice. Minimum gel width was measured each week for all constructs.

The gel with 15% GFC added had the greatest retention of cells at threeweeks (one factor ANOVA, p=0.05; Fisher's PLSD with significantdifferences between groups 1 and 2), suggesting this percentage of GFCis optimal for cell retention and support in the gel. Rates of collagensynthesis were also highest in this group at 2 and 3 weeks of culture.The addition of 15% by volume of the “growth factor cocktail”significantly increased the DNA retention in the gel and also resultedin increased rates of collagen synthesis in the gel.

Other Embodiments

While the invention has been described in conjunction with the detaileddescription thereof, the foregoing description is intended to illustrateand not limit the scope of the invention, which is defined by the scopeof the appended claims. Other aspects, advantages, and modifications arewithin the scope of the following claims.

1. A scaffold for repair of a tissue defect in comprising athree-dimensional matrix adapted to facilitate cell in-growth, whereinsaid matrix is shaped for implantation into a patient at the site of thetissue defect, wherein said matrix comprises a natural matrix materialwherein the natural matrix material is a collagen glycosaminoglycancopolymer comprised of collagen type I, and wherein said scaffoldfurther comprises plasma.
 2. The scaffold according to claim 1, whereinthe tissue defect is extra-articular.
 3. The scaffold according to claim1, wherein said tissue defect is intra-articular.
 4. The scaffoldaccording to claim 1, wherein said tissue defect comprises a ligament.5. The scaffold according to claim 1, wherein said tissue defectcomprises a tendon.
 6. The scaffold according to claim 1, wherein saidtissue defect comprises bone.
 7. A scaffold for repair of a tissuedefect in comprising a three-dimensional matrix adapted to facilitatecell in-growth, wherein said matrix is shaped for implantation into apatient at the site of the tissue defect, wherein said matrix comprisesa natural matrix material wherein the natural matrix material is acollagen glycosaminoglycan copolymer comprised of collagen type I, andwherein said scaffold further comprises a platelet.
 8. The scaffoldaccording to claim 7, wherein said tissue defect is extra-articular. 9.The scaffold according to claim 7, wherein said tissue defect isintra-articular.
 10. The scaffold according to claim 7, wherein saidtissue defect comprises a ligament.
 11. The scaffold according to claim7, wherein said tissue defect comprises a tendon.
 12. A scaffold forrepair of a tissue defect in comprising a three-dimensional matrixadapted to facilitate cell in-growth, wherein said matrix is shaped forimplantation into a patient at the site of the tissue defect, whereinsaid matrix comprises a natural matrix material wherein the naturalmatrix material is a collagen glycosaminoglycan copolymer comprised ofcollagen type I, and wherein said scaffold further comprises aneutralizing agent.
 13. The scaffold according to claim 12, wherein saidtissue defect is extra-articular.
 14. The scaffold according to claim12, wherein said tissue defect is intra-articular.
 15. The scaffoldaccording to claim 12, wherein said tissue defect is a partial orcomplete tear of a ligament.
 16. The scaffold according to claim 12,wherein said tissue defect is a partial or complete tear of an anteriorcruciate ligament (ACL).
 17. The scaffold according to claim 12, whereinsaid tissue defect is a partial or complete tear of the rotator cuff.18. The scaffold according to claim 12, wherein said tissue defect is apartial or complete tear of the labrum.
 19. The scaffold according toclaim 12, wherein said tissue defect is a partial or complete tear ofthe meniscus.